CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Transition impact of adopting ASC 326	Common Stock	Additional Paid-In Capital	Retained Earnings	Retained Earnings Transition impact of adopting ASC 326	Accumulated Other Comprehensive Income/ (Loss)
Balance at beginning of period at Dec. 31, 2017	$ 563,816		$ 23,996	$ 168,188	$ 378,489		$ (6,857)
Net income	100,864				100,864
Other comprehensive loss, net of tax	(7,420)						(7,420)
Total other comprehensive income	93,444
Common stock dividends	(39,277)				(39,277)
Stock compensation expense	2,645			2,645
Acquisition	441		21	420
Stock option plan	446,640		11,446	435,194
Employee stock purchase plan	954		29	925
Restricted stock, net	(760)		39	(799)
Reclassification of tax effects from other comprehensive income/ (loss)	0				1,477		(1,477)
Balance at end of period at Dec. 31, 2018	1,067,903		35,531	606,573	441,553		(15,754)
Net income	116,433				116,433
Other comprehensive loss, net of tax	11,422						11,422
Total other comprehensive income	127,855
Common stock dividends	(42,272)				(42,272)
Stock compensation expense	3,042			3,042
Acquisition	334		15	319
Directors stock purchase plan	30		1	29
Employee stock purchase plan	1,069		37	1,032
Restricted stock, net	(703)		54	(757)
Repurchase of common stock	(24,284)		(668)	(23,616)
Balance at end of period at Dec. 31, 2019	1,132,974		34,970	586,622	515,714		(4,332)
Net income	96,953				96,953
Other comprehensive loss, net of tax	23,037						23,037
Total other comprehensive income	119,990
Common stock dividends	(53,175)				(53,175)
Stock compensation expense	3,850			3,850
Acquisition	316		27	289
Stock option plan	289,089		12,769	276,320
Conversion of stock options	3,611			3,611
Employee stock purchase plan	1,681		65	1,616
Restricted stock, net	(458)		46	(504)
Repurchase of common stock	(25,702)		(820)	(24,882)
Adoption of ASC 326 - Financial Instruments - Credit Losses		$ (2,221)				$ (2,221)
Balance at end of period at Dec. 31, 2020	$ 1,469,955		$ 47,057	$ 846,922	$ 557,271		$ 18,705
Accounting Standards Update [Extensible List]	Adoption of ASC 326 - Financial Instruments - Credit Losses