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	(5,954)
Issuance of common stock		0	0
Tax benefit from share-based compensation			115
Equity compensation			6,017
Reacquisition of convertible junior subordinated debentures-equity component			(6,337)
Reissuance of treasury stock, net				0		0
Other comprehensive income, net of tax	$ 105,720				105,720
Net income	178,412					178,412
Balance, end of period at Jun. 30, 2016	2,515,092	341,076	1,664,079	(3,362)	44,840	468,459
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	(7,494)
Issuance of common stock		10,386	60,903
Tax benefit from share-based compensation			0
Equity compensation			6,855
Reacquisition of convertible junior subordinated debentures-equity component			0
Reissuance of treasury stock, net				150,359		(21,740)
Other comprehensive 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