| Note 24 - Parent Company Financial Information (Tables)
 | 12 Months Ended | 
| Dec. 31, 2017 | 
|---|
| Notes Tables |  | 
| Condensed Balance Sheet [Table Text Block] |   |  |  | December 31, 2017 |  | December 31, 2016 |   | ASSETS |  |  |  |  |  |  |  |  |   | Cash and due from banks |  | $ | 9,891 |  |  | $ | 6,060 |  |   | Investment in subsidiary |  |  | 665,192 |  |  |  | 574,261 |  |   | Other assets |  |  | 368 |  |  |  | 375 |  |   | Total assets |  | $ | 675,451 |  |  | $ | 580,696 |  |   |  |  |  |  |  |  |  |  |  |   | LIABILITIES AND STOCKHOLDERS' EQUITY |  |  |  |  |  |  |  |  |   | Liabilities: |  |  |  |  |  |  |  |  |   | Other borrowings |  | $ | 64,632 |  |  | $ | 54,663 |  |   | Other liabilities |  |  | 3,717 |  |  |  | 3,521 |  |   | Total liabilities |  |  | 68,349 |  |  |  | 58,184 |  |   | Stockholders' equity: |  |  |  |  |  |  |  |  |   | Preferred stock, Series A Senior Non-Cumulative Perpetual, par value $0.001 (liquidation preference $1,000), net of discount; no shares authorized, issued and outstanding at December 31, 2017, and December 31, 2016 |  |  | - |  |  |  | - |  |   | Preferred stock, par value $0.001 per share; 1,000,000 authorized and undesignated at December 31, 2017 and December 31, 2016 |  |  | - |  |  |  | - |  |   | Common stock, par value $0.001 per share; 100,000,000 shares authorized; 52,992,586 shares issued and outstanding at December 31, 2017 and 52,636,896 shares issued and outstanding at December 31, 2016 |  |  | 53 |  |  |  | 53 |  |   | Additional paid-in capital |  |  | 217,693 |  |  |  | 215,932 |  |   | Retained earnings |  |  | 389,554 |  |  |  | 307,151 |  |   | Accumulated other comprehensive (loss) income |  |  | (198 | ) |  |  | (624 | ) |   | Total stockholders' equity |  |  | 607,102 |  |  |  | 522,512 |  |   | Total liabilities and stockholders' equity |  | $ | 675,451 |  |  | $ | 580,696 |  |  | 
| Condensed Income Statement [Table Text Block] |   |  |  | 2017 |  | 2016 |  | 2015 |   | Income: |  |  |  |  |  |  |  |  |  |  |  |  |   | Dividends received from subsidiary |  | $ | 6,500 |  |  | $ | 2,500 |  |  | $ | 20,000 |  |   | Other income |  |  | 2 |  |  |  | 2 |  |  |  | 1 |  |   | Total income |  |  | 6,502 |  |  |  | 2,502 |  |  |  | 20,001 |  |   | Expense: |  |  |  |  |  |  |  |  |  |  |  |  |   | Other expenses |  |  | 2,260 |  |  |  | 2,208 |  |  |  | 1,603 |  |   | Total expenses |  |  | 2,260 |  |  |  | 2,208 |  |  |  | 1,603 |  |   | Equity in undistributed earnings of subsidiary |  |  | 88,788 |  |  |  | 81,138 |  |  |  | 45,095 |  |   | Net income |  |  | 93,030 |  |  |  | 81,432 |  |  |  | 63,493 |  |   | Dividends on preferred stock |  |  | - |  |  |  | - |  |  |  | 233 |  |   | Net income available to common stockholders |  | $ | 93,030 |  |  | $ | 81,432 |  |  | $ | 63,260 |  |  | 
| Condensed Cash Flow Statement [Table Text Block] |   |  |  | 2017 |  | 2016 |  | 2015 |   | Operating activities |  |  |  |  |  |  |  |  |  |  |  |  |   | Net income |  | $ | 93,030 |  |  | $ | 81,432 |  |  | $ | 63,493 |  |   | Adjustments to reconcile net income to net cash used in operating activities: |  |  |  |  |  |  |  |  |  |  |  |  |   | Other |  |  | (314 | ) |  |  | 1,442 |  |  |  | (271 | ) |   | Equity in undistributed earnings of subsidiary |  |  | (88,788 | ) |  |  | (81,138 | ) |  |  | (45,095 | ) |   | Net cash provided by operating activities |  |  | 3,928 |  |  |  | 1,736 |  |  |  | 18,127 |  |   | Investing activities |  |  |  |  |  |  |  |  |  |  |  |  |   | Investment in subsidiary |  |  | - |  |  |  | (36,000 | ) |  |  | - |  |   | Net cash paid in acquisition |  |  | - |  |  |  | - |  |  |  | (20,926 | ) |   | Other |  |  | - |  |  |  | - |  |  |  | 736 |  |   | Net cash used in investing activities |  |  | - |  |  |  | (36,000 | ) |  |  | (20,190 | ) |   | Financing activities |  |  |  |  |  |  |  |  |  |  |  |  |   | Proceeds from issuance of subordinated notes |  |  | 29,943 |  |  |  | - |  |  |  | 34,750 |  |   | Redemption of subordinated notes |  |  | (20,000 | ) |  |  | - |  |  |  | - |  |   | Redemption of preferred stock |  |  | - |  |  |  | - |  |  |  | (40,000 | ) |   | Dividends paid on common stock |  |  | (10,040 | ) |  |  | (7,858 | ) |  |  | (5,883 | ) |   | Dividends paid on preferred stock |  |  | - |  |  |  | - |  |  |  | (233 | ) |   | Net cash provided by financing activities |  |  | (97 | ) |  |  | (7,858 | ) |  |  | (11,366 | ) |   | Increase (decrease) in cash and cash equivalents |  |  | 3,831 |  |  |  | (42,122 | ) |  |  | (13,429 | ) |   | Cash and cash equivalents at beginning of year |  |  | 6,060 |  |  |  | 48,182 |  |  |  | 61,611 |  |   | Cash and cash equivalents at end of year |  | $ | 9,891 |  |  | $ | 6,060 |  |  | $ | 48,182 |  |  |