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		771	(7,494)
Issuance of common stock		10,386	60,903
Equity compensation			6,855
Repurchase of common stock				0
Reissuance of treasury stock, net				150,359		(21,740)
Other comprehensive (loss) income, net of tax	$ 37,606				37,606
Net income	208,420					208,420
Balance, end of period at Jun. 30, 2017	2,995,061	370,557	1,842,601	0	(37,494)	819,397
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		781	(8,854)
Issuance of common stock		0	0
Equity compensation			10,523
Repurchase of common stock				(100,059)
Reissuance of treasury stock, net				0		0
Other comprehensive (loss) income, net of tax	(73,493)				(73,493)
Net income	330,451					330,451
Balance, end of period at Jun. 30, 2018	$ 3,313,875	$ 371,348	$ 1,852,251	$ (100,059)	$ (117,294)	$ 1,307,629