Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Net Investment	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2015	$ 2,788,200				$ (51,259)	$ 2,736,941
Balance (in shares) at Dec. 31, 2015		139,459,620
Increase (Decrease) in Stockholders' Equity
Net income	65,531					65,531
Distributions	(363,624)					(363,624)
Other comprehensive income, net of tax					32,886	32,886
Balance at Mar. 31, 2016	$ 2,490,107				(18,373)	2,471,734
Balance (in shares) at Mar. 31, 2016		139,459,620
Balance at Dec. 31, 2016		$ 1,395	$ 2,484,251	$ 78,850	(88,011)	$ 2,476,485
Balance (in shares) at Dec. 31, 2016		139,530,654				139,530,654
Increase (Decrease) in Stockholders' Equity
Net income				56,740		$ 56,740
Cash dividends declared ($0.22 per share)				(30,700)		(30,700)
Common stock issued under Employee Stock Purchase Plan			528			528
Common stock issued under Employee Stock Purchase Plan (in shares)		15,961
Equity-based awards			1,817	(195)		1,622
Other comprehensive income, net of tax					1,319	1,319
Balance at Mar. 31, 2017		$ 1,395	$ 2,486,596	$ 104,695	$ (86,692)	$ 2,505,994
Balance (in shares) at Mar. 31, 2017		139,546,615				139,546,615