| Condensed Financial Information of Parent Company (Tables)
 | 12 Months Ended | 
| Dec. 31, 2020 | 
|---|
| Condensed Financial Information Of Parent Company Only Disclosure [Abstract] |  | 
| Balance Sheets of Parent Company | Balance Sheets   
|   |   | Year Ended December 31, |   |  
|   |   | 2020 |   |   | 2019 |   |  
|   |   | (in thousands) |   |  
| Assets |   |   |   |   |   |   |   |   |  
| Cash |   | $ | 17,266 |   |   | $ | 17,105 |   |  
| Investments in consolidated subsidiaries |   |   | 679,455 |   |   |   | 658,464 |   |  
| Other assets |   |   | 995 |   |   |   | 7,511 |   |  
| Total assets |   | $ | 697,716 |   |   | $ | 683,080 |   |  
| Liabilities and stockholders' equity |   |   |   |   |   |   |   |   |  
| Liabilities |   |   |   |   |   |   |   |   |  
| Subordinated debentures |   | $ | 118,972 |   |   | $ | 118,377 |   |  
| Other liabilities |   |   | 1,701 |   |   |   | 1,436 |   |  
| Total liabilities |   |   | 120,673 |   |   |   | 119,813 |   |  
| Stockholders' equity |   |   | 577,043 |   |   |   | 563,267 |   |  
| Total liabilities and stockholders' equity |   | $ | 697,716 |   |   | $ | 683,080 |   |  | 
| Statement of Income of Parent Company | Statements of Income   
|   |   | Year Ended December 31, |   |  
|   |   | 2020 |   |   | 2019 |   |   | 2018 |   |  
|   |   | (in thousands) |   |  
| Dividends from bank subsidiaries |   | $ | 16,986 |   |   | $ | 44,500 |   |   | $ | 76,669 |   |  
| Interest expense |   |   | (6,607 | ) |   |   | (7,032 | ) |   |   | (6,925 | ) |  
| Other expense |   |   | (4,892 | ) |   |   | (5,333 | ) |   |   | (5,988 | ) |  
| Income before taxes and undistributed income of subsidiary |   |   | 5,487 |   |   |   | 32,135 |   |   |   | 63,756 |   |  
| Income tax benefit |   |   | 3,247 |   |   |   | 3,823 |   |   |   | 4,116 |   |  
| Income before undistributed income of subsidiary |   |   | 8,734 |   |   |   | 35,958 |   |   |   | 67,872 |   |  
| Equity in undistributed income of subsidiary |   |   | 33,463 |   |   |   | (3,170 | ) |   |   | (10,004 | ) |  
| Net income |   | $ | 42,197 |   |   | $ | 32,788 |   |   | $ | 57,868 |   |  | 
| Statement of Cash Flows of Parent Company | Statements of Cash Flows   
|   |   | Year Ended December 31, |   |  
|   |   | 2020 |   |   | 2019 |   |   | 2018 |   |  
|   |   | (in thousands) |   |  
| Cash Flows from Operating Activities: |   |   |   |   |   |   |   |   |   |   |   |   |  
| Net income |   | $ | 42,197 |   |   | $ | 32,788 |   |   | $ | 57,868 |   |  
| Adjustments to reconcile net income to net cash used in operating activities |   |   |   |   |   |   |   |   |   |   |   |   |  
| Undistributed income of subsidiary |   |   | (33,463 | ) |   |   | 3,170 |   |   |   | 10,004 |   |  
| Amortization of subordinated debentures |   |   | 595 |   |   |   | 569 |   |   |   | 538 |   |  
| Share-based compensation expense |   |   | 2,544 |   |   |   | 3,125 |   |   |   | 3,515 |   |  
| Change in other assets and liabilities |   |   | 6,779 |   |   |   | 4,679 |   |   |   | (10,463 | ) |  
| Net cash provided by (used in) operating activities |   |   | 18,651 |   |   |   | 44,331 |   |   |   | 61,462 |   |  
| Cash Flows from Financing Activities: |   |   |   |   |   |   |   |   |   |   |   |   |  
| Proceeds from exercise of stock options |   |   | — |   |   |   | 2,979 |   |   |   | 570 |   |  
| Cash paid for repurchase of vested shares due to employee tax liability |   |   | (335 | ) |   |   | (517 | ) |   |   | (680 | ) |  
| Repurchase of common stock |   |   | (2,196 | ) |   |   | (7,362 | ) |   |   | (36,068 | ) |  
| Cash dividends paid |   |   | (15,959 | ) |   |   | (29,776 | ) |   |   | (30,921 | ) |  
| Net cash provided by (used in) financing activities |   |   | (18,489 | ) |   |   | (34,676 | ) |   |   | (67,099 | ) |  
| Net increase (decrease) in cash |   |   | 162 |   |   |   | 9,655 |   |   |   | (5,637 | ) |  
| Cash at beginning of year |   |   | 17,105 |   |   |   | 7,450 |   |   |   | 13,087 |   |  
| Cash at end of year |   | $ | 17,266 |   |   | $ | 17,105 |   |   | $ | 7,450 |   |  |