Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred stock	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive loss	Treasury stock
Balance (in shares)		150,000
Balance (in shares)			195,843,297
Treasury stock (in shares)							(538,921)
Balance at Dec. 31, 2016	$ 2,316,244	$ 15,000	$ 195,843	$ 1,232,478	$ 912,282	$ (35,733)	$ (3,626)
Net Income					37,325
Net Income	37,325
Other comprehensive income	(452)					(452)
Dividends declared on preferred stocks	(171)				(171)
Dividends declared on common stock	(37,596)				(37,596)
Stock-based compensation	996			1,134	(138)
Repurchase of common stock							(64,384)
Repurchase of common stock	(1,684)						$ (1,684)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings				(2,441)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)							64,384
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings							$ 1,684
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(757)
Balance at Mar. 31, 2017	$ 2,313,905	$ 15,000	$ 195,843	1,231,171	911,702	(36,185)	$ (3,626)
Balance (in shares)		150,000
Balance (in shares)	195,843,297		195,843,297
Treasury stock (in shares)	(538,921)						(538,921)
Balance (in shares)	195,843,297		195,843,297
Treasury stock (in shares)	(538,921)						(538,921)
Cumulative effect of adoption of ASU 2014-09 | Accounting Standards Update 2014-09	$ (970)				(970)
Adjusted balance at January 1, 2018	2,428,073		$ 195,843	1,233,412	1,039,778	(37,334)	$ (3,626)
Balance at Dec. 31, 2017	2,429,043		195,843	1,233,412	1,040,748	(37,334)	$ (3,626)
Net Income					42,437
Net Income	42,437
Other comprehensive income	433					433
Reclassification of certain prior period tax effects from accumulated other comprehensive loss | Adjustments for new accounting pronouncement	(7,900)				7,959	(7,959)
Dividends declared on common stock	(38,572)				(38,572)
Stock-based compensation	1,090			1,223	(133)
Repurchase of common stock							(182,424)
Repurchase of common stock	(5,020)						$ (5,020)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings				(7,350)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings (in shares)							182,424
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings							$ 5,020
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(2,330)
Balance at Mar. 31, 2018	$ 2,426,111		$ 195,843	$ 1,227,285	$ 1,051,469	$ (44,860)	$ (3,626)
Balance (in shares)	195,843,297		195,843,297
Treasury stock (in shares)	(538,921)						(538,921)