Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	Unallocated ESOP Shares	Common Stock Acquired By DDFP	Deferred Compensation DDFP
Balance at the beginning of the period at Dec. 31, 2016	$ 1,251,781	$ 832	$ 1,005,777	$ 550,768	$ (3,397)	$ (264,221)	$ (37,978)	$ (5,846)	$ 5,846
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	93,949			93,949
Current period change in other comprehensive income (loss)	(2,673)				(2,673)
Cash dividends paid	(59,980)			(59,980)
Distributions from DDFP	232		232					671	(671)
Purchases of treasury stock	(443)					(443)
Purchase of employee restricted shares to fund statutory tax withholding	(778)					(778)
Shares issued dividend reinvestment plan	2,114		712			1,402
Option exercises	2,954		(1,179)			4,133
Allocation of ESOP shares	6,339		2,200				4,139
Allocation of Stock Award Plan ("SAP") shares	4,963		4,963
Allocation of stock options	203		203
Balance at the end of the period at Dec. 31, 2017	1,298,661	832	1,012,908	586,132	(7,465)	(259,907)	(33,839)	(5,175)	5,175
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	118,387			118,387
Current period change in other comprehensive income (loss)	(4,687)				(4,687)
Cash dividends paid	(53,604)			(53,604)
Effect of adopting ASU No. 2016-02					(184)
Distributions from DDFP	156		156					671	(671)
Purchases of treasury stock	(13,172)					(13,172)
Purchase of employee restricted shares to fund statutory tax withholding	(1,896)					(1,896)
Shares issued dividend reinvestment plan	1,709		577			1,132
Option exercises	1,007		(366)			1,373
Allocation of ESOP shares	6,183		2,022				4,161
Allocation of Stock Award Plan ("SAP") shares	6,046		6,046
Allocation of stock options	190		190
Balance at the end of the period 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	112,633			112,633
Current period change in other comprehensive income (loss)	16,157				16,157
Cash dividends paid	(72,809)			(72,809)
Effect of adopting ASU No. 2016-02					0
Distributions from DDFP	164		164					671	(671)
Purchases of treasury stock	(19,867)					(19,867)
Purchase of employee restricted shares to fund statutory tax withholding	(1,985)					(1,985)
Shares issued dividend reinvestment plan	2,230		671			1,559
Reclass of stock award shares	0		(24,024)			24,024
Option exercises	139		(96)			235
Allocation of ESOP shares	6,996		2,203				4,793
Allocation of Stock Award Plan ("SAP") shares	6,671		6,671
Allocation of stock options	181		181
Balance at the end of the period at Dec. 31, 2019	$ 1,413,840	$ 832	$ 1,007,303	$ 695,273	$ 3,821	$ (268,504)	$ (24,885)	$ (3,833)	$ 3,833