Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect Adjustment [Member]		Common Stock	Capital Surplus	Retained Earnings	Retained Earnings Cumulative Effect Adjustment [Member]		Accumulated Other Comprehensive (Loss) Income	Treasury Stock
Beginning Balance at Dec. 31, 2018	$ 2,228,470			$ 55,057	$ 1,054,601	$ 1,488,421			$ (95,782)	$ (273,827)
Total comprehensive income	273,102					114,703			158,399
Dividends	(29,538)					(29,538)
Purchase of treasury stock	(4,114)									(4,114)
Forfeitures of equity awards, net of issuances	604				3,107					(2,503)
Recognition of equity-based compensation	7,006				7,006
Sale of treasury stock	459				185					274
Exercise of stock options	1,801				402					1,399
Ending Balance at Jun. 30, 2019	2,477,790			55,057	1,065,301	1,573,586			62,617	(278,771)
Beginning Balance at Mar. 31, 2019	2,350,843			55,057	1,060,630	1,531,396			(17,639)	(278,601)
Total comprehensive income	137,215					56,959			80,256
Dividends	(14,769)					(14,769)
Purchase of treasury stock	(28)									(28)
Forfeitures of equity awards, net of issuances					724					(724)
Recognition of equity-based compensation	3,717				3,717
Sale of treasury stock	198				85					113
Exercise of stock options	614				145					469
Ending Balance at Jun. 30, 2019	2,477,790			55,057	1,065,301	1,573,586			62,617	(278,771)
Beginning Balance at Dec. 31, 2019	2,606,440	$ (7,039)	[1]	55,057	1,073,764	1,672,438	$ (7,039)	[1]	83,180	(277,999)
Total comprehensive income	258,172					57,090			201,082
Dividends	(30,200)					(30,200)
Purchase of treasury stock	(59,459)				615					(60,074)
Forfeitures of equity awards, net of issuances	593				676					(83)
Recognition of equity-based compensation	6,109				6,109
Sale of treasury stock	321				120					201
Exercise of stock options	2,458				429					2,029
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member					us-gaap:AccountingStandardsUpdate201613Member
Ending Balance at Jun. 30, 2020	2,777,395			55,057	1,081,713	1,692,289			284,262	(335,926)
Beginning Balance at Mar. 31, 2020	2,663,441			55,057	1,073,089	1,646,751			219,390	(330,846)
Total comprehensive income	125,401					60,529			64,872
Dividends	(14,991)					(14,991)
Purchase of treasury stock	(73)				5,115					(5,188)
Forfeitures of equity awards, net of issuances					155					(155)
Recognition of equity-based compensation	3,292				3,292
Sale of treasury stock	137				25					112
Exercise of stock options	188				37					151
Ending Balance at Jun. 30, 2020	$ 2,777,395			$ 55,057	$ 1,081,713	$ 1,692,289			$ 284,262	$ (335,926)

[1] Related to the adoption of ASU No. 2016-13. See Note 3, “New Accounting Pronouncements,” for further detail.