CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Paid-in capital	Treasury stock	Accumulated other comprehensive (loss) income	Retained earnings
Balance, beginning of period at Dec. 31, 2016		$ 359,400	$ 1,782,337	$ (150,359)	$ (75,100)	$ 632,717
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net common stock issued under share-based compensation plans		776	(7,558)
Issuance of common stock		10,386	60,903
Equity compensation			10,578
Repurchase of common stock				0
Reissuance of treasury stock, net				150,359		(21,740)
Other comprehensive (loss) income, net of tax	$ 49,003				49,003
Net income	328,447					328,447
Balance, end of period at Sep. 30, 2017	3,130,149	370,562	1,846,260	0	(26,097)	939,424
Balance, beginning of period at Dec. 31, 2017	3,154,526	370,567	1,850,582	0	(43,801)	977,178
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net common stock issued under share-based compensation plans		786	(8,917)
Issuance of common stock		0	0
Equity compensation			15,974
Repurchase of common stock				(100,059)
Reissuance of treasury stock, net				0		0
Other comprehensive (loss) income, net of tax	(85,130)				(85,130)
Net income	512,351					512,351
Balance, end of period at Sep. 30, 2018	$ 3,489,531	$ 371,353	$ 1,857,639	$ (100,059)	$ (128,931)	$ 1,489,529