Supplementary Quarterly Financial Data (Unaudited) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 261,016	$ 257,183	$ 244,273	$ 229,403	$ 225,759	$ 197,497	$ 185,860	$ 173,154	$ 991,875	$ 782,270	$ 647,155
Cost of operations	137,832	134,459	133,971	135,775	185,450	100,193	104,253	97,718	542,037	487,614	368,687
Revenues less cost of operations	123,184	122,724	110,302	93,628	40,309	97,304	81,607	75,436	449,838	294,656	278,468
Net income	90,416	127,226	90,040	89,407	11,744	78,200	60,956	58,636	397,089	209,536	195,896
Net income attributable to common stockholders	$ 82,403	$ 118,088	$ 83,044	$ 82,592	$ 8,675	$ 71,718	$ 55,339	$ 53,742	$ 366,127	$ 189,474	$ 178,355
Earnings per common share-basic (in dollars per share)	$ 0.65	$ 0.94	$ 0.66	$ 0.66	$ 0.07	$ 0.58	$ 0.47	$ 0.46	$ 2.92	$ 1.58	$ 1.54
Earnings per common share-diluted (in dollars per share)	$ 0.65	$ 0.93	$ 0.66	$ 0.66	$ 0.07	$ 0.58	$ 0.47	$ 0.46	$ 2.91	$ 1.56	$ 1.53