Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Employee Stock Ownership Plan	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive (Loss) Gain	Treasury Stock	Common Stock Acquired by Deferred Compensation Plan	Deferred Compensation Plan Liability
Beginning Balance at Dec. 31, 2016	$ 571,903	$ (2,761)	$ 0	$ 336	$ 364,433	$ 238,192	$ (5,749)	$ (22,548)	$ (313)	$ 313
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42,470					42,470
Other comprehensive income, net of tax	400						400
Stock awards	2,181				2,181
Treasury stock allocated to restricted stock plan	0				(1,745)	822		923
Allocation of ESOP stock	919	282			637
Cash dividend	(19,286)					(19,286)
Exercise of stock options	3,354					(2,304)		5,658
Sale/Purchase of stock for the deferred compensation plan	0								229	(229)
Ending Balance at Dec. 31, 2017	601,941	(2,479)	0	336	354,377	271,023	(5,349)	(15,967)	(84)	84
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	71,932					71,932
Other comprehensive income, net of tax	1,752						1,752
Stock awards	3,038			2	3,036
Acquisition of common stock by ESOP	(8,400)	(8,400)
Allocation of ESOP stock	1,618	1,022			596
Cash dividend	(29,564)					(29,564)
Exercise of stock options	5,324			4	13,306	(8,188)		202
Acquisition of company	402,554			141	386,648			15,765
Sale/Purchase of stock for the deferred compensation plan	0								(3)	3
Purchase shares of common stock	(10,837)							(10,837)
Ending Balance at Dec. 31, 2018	1,039,358	(9,857)	0	483	757,963	305,056	(3,450)	(10,837)	(87)	87
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	88,574					88,574
Other comprehensive income, net of tax	2,242						2,242
Stock awards	3,861			2	3,859
Allocation of ESOP stock	1,575	1,209			366
Cash dividend	(34,241)					(34,241)
Exercise of stock options	1,335			2	2,054	(721)		0
Acquisition of company	76,481			32	76,449			0
Sale/Purchase of stock for the deferred compensation plan	0								(5)	5
Purchase shares of common stock	(26,066)							(26,066)
Ending Balance at Dec. 31, 2019	$ 1,153,119	$ (8,648)	$ 0	$ 519	$ 840,691	$ 358,668	$ (1,208)	$ (36,903)	$ (92)	$ 92