Summary of Quarterly Financial Information (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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 194,933	$ 192,873	$ 176,244	$ 167,293	$ 199,309	$ 186,402	$ 178,529	$ 167,271	$ 182,297	$ 186,547	$ 176,349	$ 164,333	$ 731,343	$ 731,511	$ 709,526
Operating income	47,112	45,279	36,239	26,076	58,490	48,538	49,665	34,164	50,191	56,008	50,659	36,045	154,706	190,857	192,903
Net income	28,720	26,784	18,930	9,856	39,781	29,230	30,184	18,058	32,260	35,489	31,359	19,145	$ 84,290	$ 117,253	$ 118,253
Net income attributable to common stockholders	$ 16,799	$ 15,882	$ 11,087	$ 5,677	$ 22,842	$ 16,342	$ 16,651	$ 9,768	$ 17,272	$ 18,806	$ 16,584	$ 9,985
Basic and diluted net income per share attributable to common stockholders (USD per share)	$ 0.09	$ 0.09	$ 0.06	$ 0.03	$ 0.13	$ 0.10	$ 0.10	$ 0.06	$ 0.11	$ 0.12	$ 0.10	$ 0.06