Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Unallocated ESOP Shares	Common Stock Acquired By Directors Deferred Fee Plan	Deferred Compensation DDFP
Balance at December 31, at Dec. 31, 2018	$ 1,358,980	$ 832	$ 1,021,533	$ 651,099	$ (12,336)	$ (272,470)	$ (29,678)	$ (4,504)	$ 4,504
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	30,890			30,890
Other comprehensive income (loss), net of tax	7,252				7,252
Cash dividends paid	(28,964)			(28,964)
Distributions from Deferred directors fee plan ("DDFP")	42		42					167	(167)
Purchases of treasury stock	(180)					(180)
Purchase of employee restricted shares to fund statutory tax withholding	(1,914)					(1,914)
Shares issued dividend reinvestment plan	840		307			533
Stock option exercises	15		(11)			26
Allocation of ESOP shares	1,075		370				705
Allocation of SAP shares	1,388		1,388
Allocation of stock options	42		42
Balance at March 31, at Mar. 31, 2019	1,373,816	832	1,023,671	657,375	(5,084)	(274,005)	(28,973)	(4,337)	4,337
Balance at December 31, 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 Deferred directors fee plan ("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 SAP shares	993		993
Allocation of stock options	47		47
Balance at March 31, at Mar. 31, 2020	$ 1,412,589	$ 832	$ 1,008,582	$ 686,397	$ 14,938	$ (274,044)	$ (24,116)	$ (3,666)	$ 3,666