Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period	$ 178,721	$ 77,259
Net income	58,046	80,612
Other comprehensive income	48,793	(62,491)
Common	(36,010)	(37,815)
Issuance of common stock	(4,134)	(7,666)
Conversion to common stock		0
Stock-based compensation expense	6,303	5,036
Repurchase of common stock	(128,451)
Balances, end of period	123,268	54,935
Preferred stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period	1	1
Conversion to common stock		0
Balances, end of period	1	1
Preference stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period	505	548
Conversion to common stock	(13)	(5)
Balances, end of period	492	543
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period	323,338	323,338
Balances, end of period	323,338	323,338
Additional paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period	161,280	178,852
Issuance of common stock	(21,555)	(30,914)
Conversion to common stock	(273)	(105)
Stock-based compensation expense	6,303	5,036
Balances, end of period	145,755	152,869
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period	5,155,537	4,897,708
Net income	58,046	80,612
Common	(36,010)	(37,815)
Balances, end of period	5,177,573	4,940,505
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period	(888,635)	(846,156)
Other comprehensive income	48,793	(62,491)
Balances, end of period	(839,842)	(908,647)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period	(4,573,305)	(4,477,032)
Issuance of common stock	17,421	23,248
Conversion to common stock	286	110
Repurchase of common stock	(128,451)
Balances, end of period	$ (4,684,049)	$ (4,453,674)