Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE INCOME	TREASURYSTOCK	UNALLOCATED ESOP SHARES	COMMON STOCK ACQUIRED BY DEFERRED COMP PLANS	DEFERRED COMPENSATION PLANS
Beginning balance at Dec. 31, 2019	$ 1,413,840	$ 832	$ 1,007,303	$ 695,273	$ 3,821	$ (268,504)	$ (24,885)	$ (3,833)	$ 3,833
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	14,931			14,931
Other comprehensive income (loss), net of tax	11,117				11,117
Cash dividends paid	(15,496)			(15,496)
Distributions from DDFP	37		37					167	(167)
Purchases of treasury stock	(4,985)					(4,985)
Purchase of employee restricted shares to fund statutory tax withholding	(956)					(956)
Shares issued dividend reinvestment plan	451		50			401
Allocation of ESOP shares	921		152				769
Allocation of Stock Award Plan ("SAP") shares	993		993
Allocation of stock options	47		47
Ending Balance at Mar. 31, 2020	1,412,589	832	1,008,582	686,397	14,938	(274,044)	(24,116)	(3,666)	3,666
Beginning balance at Dec. 31, 2020	1,619,797	832	962,453	718,090	17,655	(59,018)	(20,215)	(4,549)	4,549
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	48,559			48,559
Other comprehensive income (loss), net of tax	(4,678)				(4,678)
Cash dividends paid	(18,075)			(18,075)
Distributions from DDFP	28		28					168	(168)
Purchases of treasury stock	(48)					(48)
Purchase of employee restricted shares to fund statutory tax withholding	(915)					(915)
Shares issued dividend reinvestment plan	0
Stock option exercises	638		(82)			720
Allocation of ESOP shares	913		145				768
Allocation of Stock Award Plan ("SAP") shares	959		959
Allocation of stock options	53		53
Ending Balance at Mar. 31, 2021	$ 1,647,231	$ 832	$ 963,556	$ 748,574	$ 12,977	$ (59,261)	$ (19,447)	$ (4,381)	$ 4,381