Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Loss	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)		(15,080)			56,786	(71,866)
Reclassification of certain tax effects	[1]	12,917			12,917
Dividends		(14,473)			(14,473)
Purchase of treasury stock		(5,951)					(5,951)
Issuance of equity awards, net of forfeitures		495		(2,959)			3,454
Recognition of equity-based compensation		2,270		2,270
Sale of treasury stock		285		145			140
Exercise of stock options		5,247		1,122			4,125
Cumulative effect adjustments | ASU Nos. 2016-01 and 2017-12 [Member]	[2]	145			145
Ending Balance at Mar. 31, 2018		2,167,386	55,057	1,046,673	1,393,485	(117,391)	(210,438)
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)		135,887			57,744	78,143
Dividends		(14,769)			(14,769)
Purchase of treasury stock		(4,086)					(4,086)
Issuance of equity awards, net of forfeitures		604		2,383			(1,779)
Recognition of equity-based compensation		3,289		3,289
Sale of treasury stock		261		100			161
Exercise of stock options		1,187		257			930
Ending Balance at Mar. 31, 2019		$ 2,350,843	$ 55,057	$ 1,060,630	$ 1,531,396	$ (17,639)	$ (278,601)

[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.