Selected Quarterly Data (Unaudited) - Summary of Selected Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 171,646	$ 154,790	$ 132,894	$ 144,566	$ 146,084	$ 145,955	$ 140,489	$ 130,718
Operating Income (Loss)	50,931	41,009	26,622	24,602	37,796	35,787	30,128	20,999	$ 143,164	$ 124,710	$ 113,099
Net income (loss)	61,814	40,934	16,209	1,006	29,782	25,359	27,899	22,468	119,963	105,508	76,080
Net Income (Loss) Attributable to Common Stockholders	$ 43,315	$ 29,648	$ 11,279	$ (4,285)	$ 20,808	$ 22,000	$ 24,842	$ 19,662	$ 79,957	$ 87,312	$ 67,192
Earnings (loss) per share—Basic (in dollars per share)	$ 5.67	$ 3.86	$ 1.46	$ (0.58)	$ 3.02	$ 3.17	$ 3.55	$ 2.80	$ 10.49	$ 12.54	$ 9.37
Earnings (loss) per share—Diluted (in dollars per share)	$ 5.40	$ 3.71	$ 1.43	$ (0.58)	$ 2.83	$ 2.95	$ 3.26	$ 2.61	$ 10.02	$ 11.74	$ 8.86