Consolidated Statements of Changes in Shareholders’ Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings (Deficit)	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2014	$ 1,720,335	$ 810	$ 1,565,180	$ 192,805	$ (38,460)
Beginning Balance (in shares) at Dec. 31, 2014		80,983,249
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares to stockholders, directors and employees		$ 3	(3)
Issuance of common shares to stockholders, directors and employees (in shares)		306,593
Repurchase of common shares from stockholders, directors and employees	(20,881)	$ (11)	(20,870)
Repurchase of common shares from stockholders', directors and employees (in shares)		(1,057,582)
Amortization of share-based payments	5,537		5,537
Excess tax benefit from stock based compensation	493		493
Dividends declared	(72,960)			(72,960)
Net income	121,729			121,729
Net change in fair value of derivatives, net of tax expense of $0, $0 and $35, respectively	1,224				1,224
Net derivative loss reclassified into earnings	24,023				24,023
Beginning Balance (in shares) at Dec. 31, 2015		80,232,260
Beginning Balance at Dec. 31, 2015	1,779,500	$ 802	1,550,337	241,574	(13,213)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares to stockholders, directors and employees	0	$ 3	(3)
Issuance of common shares to stockholders, directors and employees (in shares)		317,501
Repurchase of common shares from stockholders, directors and employees	(37,337)	$ (19)	(37,318)
Repurchase of common shares from stockholders', directors and employees (in shares)		(1,956,628)
Amortization of share-based payments	7,901		7,901
Excess tax benefit from stock based compensation	273		273
Dividends declared	(77,137)			(77,137)
Net income	151,453			151,453
Net change in fair value of derivatives, net of tax expense of $0, $0 and $35, respectively	(1)				(1)
Net derivative loss reclassified into earnings	$ 9,662				9,662
Beginning Balance (in shares) at Dec. 31, 2016	78,593,133	78,593,133
Beginning Balance at Dec. 31, 2016	$ 1,834,314	$ 786	1,521,190	315,890	(3,552)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares to stockholders, directors and employees		$ 3	(3)
Issuance of common shares to stockholders, directors and employees (in shares)		344,017
Repurchase of common shares from stockholders, directors and employees	(4,862)	$ (2)	(4,860)
Repurchase of common shares from stockholders', directors and employees (in shares)		(229,187)
Amortization of share-based payments	11,469		11,469
Dividends declared	(83,433)			(83,433)
Net income	147,874			147,874
Net change in fair value of derivatives, net of tax expense of $0, $0 and $35, respectively	0
Net derivative loss reclassified into earnings	$ 2,202				(2,202)
Beginning Balance (in shares) at Dec. 31, 2017	78,707,963	78,707,963
Beginning Balance at Dec. 31, 2017	$ 1,907,564	$ 787	$ 1,527,796	$ 380,331	$ (1,350)