Quarterly Operating Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Total revenue	$ 237,519	$ 240,279	$ 257,918	$ 202,375	$ 223,407	$ 220,818	$ 237,949	$ 181,530	$ 938,091	$ 863,704	$ 870,005
Total operating expenses	75,214	211,033	211,960	185,885	189,031	176,589	200,012	168,011	684,092	733,643	730,222
Operating income	162,305	29,246	45,958	16,490	34,376	44,229	37,937	13,519
Net income	134,583	11,574	29,074	8,980	24,006	31,443	28,009	4,338	184,211	87,796	91,877
Net income attributable to common stockholders	$ 134,053	$ 11,529	$ 28,960	$ 8,945	$ 23,994	$ 31,443	$ 28,009	$ 4,338	$ 183,487	$ 87,784	$ 91,877
Net income per share available to common stockholders - basic (in dollars per share)	$ 0.67	$ 0.06	$ 0.14	$ 0.04	$ 0.12	$ 0.15	$ 0.14	$ 0.02	$ 0.91	$ 0.43	$ 0.46
Net income per share available to common stockholders - diluted (in dollars per share)	$ 0.66	$ 0.06	$ 0.14	$ 0.04	$ 0.12	$ 0.15	$ 0.14	$ 0.02	$ 0.90	$ 0.43	$ 0.46