Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands		Total	Cumulative Effect Adjustments [Member]		Adjusted Balance [Member]	Common Stock	Common Stock Adjusted Balance [Member]	Capital Surplus	Capital Surplus Adjusted Balance [Member]	Retained Earnings	Retained Earnings Cumulative Effect Adjustments [Member]		Retained Earnings Adjusted Balance [Member]	Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) Income Adjusted Balance [Member]	Treasury Stock	Treasury Stock Adjusted Balance [Member]
Beginning Balance at Dec. 31, 2017		$ 2,181,531	$ 145	[1]	$ 2,181,676	$ 55,057	$ 55,057	$ 1,046,095	$ 1,046,095	$ 1,338,110	$ 145	[1]	$ 1,338,255	$ (45,525)	$ (45,525)	$ (212,206)	$ (212,206)
Total comprehensive income (loss)		145,256								195,513				(50,257)
Reclassification of certain tax effects	[2]	12,917								12,917
Dividends		(58,264)								(58,264)
Purchase of treasury stock		(76,507)						(2,807)								(73,700)
Issuances of equity awards, net of forfeitures		495						(2,004)								2,499
Recognition of equity based compensation		10,579						10,579
Sale of treasury stock		1,062						524								538
Exercise of stock options		11,256						2,214								9,042
Ending Balance at Dec. 31, 2018		2,228,470				55,057		1,054,601		1,488,421				(95,782)		(273,827)
Total comprehensive income (loss)		422,562								243,600				178,962
Dividends		(59,583)								(59,583)
Purchase of treasury stock		(4,496)														(4,496)
Issuances of equity awards, net of forfeitures		616						3,820								(3,204)
Recognition of equity based compensation		14,234						14,234
Sale of treasury stock		831						344								487
Exercise of stock options		3,806						765								3,041
Ending Balance at Dec. 31, 2019		2,606,440	$ (7,039)	[3]	$ 2,599,401	55,057	$ 55,057	1,073,764	$ 1,073,764	1,672,438	$ (7,039)	[3]	$ 1,665,399	83,180	$ 83,180	(277,999)	$ (277,999)
Total comprehensive income (loss)		521,662								286,502				235,160
Dividends		(60,655)								(60,655)
Purchase of treasury stock		(63,766)						616								(64,382)
Issuances of equity awards, net of forfeitures		608						624								(16)
Recognition of equity based compensation		14,512						14,512
Sale of treasury stock		615						201								414
Exercise of stock options		4,571						733								3,838
Ending Balance at Dec. 31, 2020		$ 3,016,948				$ 55,057		$ 1,090,450		$ 1,891,246				$ 318,340		$ (338,145)

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

[2] Related to the adoption of ASU No. 2018-02.  See Note 2, “New Accounting Pronouncements,” for further detail.

[3] Related to the adoption of ASU No. 2016-13.  See Note 2, “New Accounting Pronouncements,” for further detail.