Selected Quarterly Data (Unaudited) - Summary of Selected Quarterly Data (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 Information Disclosure [Abstract]
Revenues	$ 146,084	$ 145,955	$ 140,489	$ 130,718	$ 138,065	$ 152,210	$ 132,932	$ 129,028
Operating Income (Loss)	37,796	35,787	30,128	20,999	29,228	33,946	27,308	22,617	$ 124,710	$ 113,099	$ 58,035
Net income (loss)	29,782	25,359	27,899	22,468	1,093	27,931	23,229	23,827	105,508	76,080	39,939
Net Income (Loss) Attributable to Common Stockholders	$ 20,808	$ 22,000	$ 24,842	$ 19,662	$ 77	$ 24,913	$ 20,986	$ 21,216	$ 87,312	$ 67,192	$ 28,676
Earnings (loss) per share—Basic (in $ per share)	$ 3.02	$ 3.17	$ 3.55	$ 2.80	$ 0.01	$ 3.47	$ 2.91	$ 2.95	$ 12.54	$ 9.37	$ 4.09
Earnings (loss) per share—Diluted (in $ per share)	$ 2.83	$ 2.95	$ 3.26	$ 2.61	$ 0.01	$ 3.19	$ 2.75	$ 2.77	$ 11.74	$ 8.86	$ 3.96