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	(7,493)
Equity compensation			3,461
Other comprehensive income, net of tax	$ 11,999				11,999
Net income	89,798					89,798
Balance, end of period at Mar. 31, 2017	2,647,531	360,171	1,778,305	(150,359)	(63,101)	722,515
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)
Equity compensation			5,272
Other comprehensive income, net of tax	(63,959)				(63,959)
Net income	143,637					143,637
Balance, end of period at Mar. 31, 2018	$ 3,231,403	$ 371,348	$ 1,847,000	$ 0	$ (107,760)	$ 1,120,815