CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Paid-in capital	Treasury stock	Accumulated other comprehensive loss	Retained earnings
Balance, beginning of period at Dec. 31, 2015		$ 340,097	$ 1,670,238	$ (3,362)	$ (60,880)	$ 290,047
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net common stock issued under share-based compensation plans		979	(5,949)
Tax benefit from share-based compensation			115
Equity compensation			3,129
Reacquisition of convertible junior subordinated debentures-equity component			(6,337)
Other comprehensive income, net of tax	$ 49,544				49,544
Net income	69,191					69,191
Balance, end of period at Mar. 31, 2016	2,346,812	341,076	1,661,196	(3,362)	(11,336)	359,238
Balance, beginning of period at Dec. 31, 2016	2,548,842	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)
Tax benefit from share-based compensation			0
Equity compensation			3,461
Reacquisition of convertible junior subordinated debentures-equity component			0
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