Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive (Loss) Income	Treasury Stock
Beginning Balance at Dec. 31, 2017		$ 2,181,531	$ 55,057	$ 1,046,095	$ 1,338,110	$ (45,525)	$ (212,206)
Total comprehensive income (loss)		28,776			112,210	(83,434)
Reclassification of certain tax effects	[1]	12,917			12,917
Dividends		(29,040)			(29,040)
Purchase of treasury stock		(6,211)					(6,211)
Issuance of equity awards, net of forfeitures		494		(2,457)			2,951
Recognition of equity-based compensation		5,201		5,201
Sale of treasury stock		553		278			275
Exercise of stock options		7,446		1,543			5,903
Cumulative effect adjustment | ASU Nos. 2016-01 and 2017-12 [Member]	[2]	145			145
Ending Balance at Jun. 30, 2018		2,201,812	55,057	1,050,660	1,434,342	(128,959)	(209,288)
Beginning Balance at Mar. 31, 2018		2,167,386	55,057	1,046,673	1,393,485	(117,391)	(210,438)
Total comprehensive income (loss)		43,856			55,424	(11,568)
Dividends		(14,567)			(14,567)
Purchase of treasury stock		(260)					(260)
Issuance of equity awards, net of forfeitures		(1)		502			(503)
Recognition of equity-based compensation		2,931		2,931
Sale of treasury stock		268		133			135
Exercise of stock options		2,199		421			1,778
Ending Balance at Jun. 30, 2018		2,201,812	55,057	1,050,660	1,434,342	(128,959)	(209,288)
Beginning Balance at Dec. 31, 2018		2,228,470	55,057	1,054,601	1,488,421	(95,782)	(273,827)
Total comprehensive income (loss)		273,102			114,703	158,399
Dividends		(29,538)			(29,538)
Purchase of treasury stock		(4,114)					(4,114)
Issuance of equity awards, net of forfeitures		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 (loss)		137,215			56,959	80,256
Dividends		(14,769)			(14,769)
Purchase of treasury stock		(28)					(28)
Issuance of equity awards, net of forfeitures				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)

[1] Related to the adoption of ASU No. 2018-02. See Note 3, “New Accounting Pronouncements,” for further detail.

[2] Related to the adoption of ASU Nos. 2016-01 and 2017-12. See Note 3, “New Accounting Pronouncements,” for further detail.