Summarized Quarterly Financial Data (Unaudited) (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
Selected Quarterly Financial Information [Abstract]
Revenues	$ 267,494	$ 239,026	$ 255,831	$ 265,302	$ 263,772	$ 241,747	$ 245,110	$ 246,508	$ 1,027,653	$ 997,137	$ 634,185
Income from operations	3,608	15,422	46,395	43,959	37,213	20,000	27,596	25,723	109,384	110,532	(22,740)
Net income (loss)	$ 5,917	$ 10,960	$ 34,152	$ 35,239	$ 28,537	$ 16,692	$ 24,409	$ 11,500	$ 86,268	$ 81,138	$ (15,671)
Net income (loss) per share:
Basic (dollars per share)	$ 0.25	$ 0.48	$ 1.57	$ 1.62	$ 1.31	$ 0.77	$ 1.12	$ 0.53	$ 3.81	$ 3.73	$ (1.03)
Diluted (dollars per share)	$ 0.25	$ 0.47	$ 1.55	$ 1.60	$ 1.29	$ 0.75	$ 1.10	$ 0.52	$ 3.77	$ 3.67	$ (1.03)