Supplemental Financial Information Quarterly Results (unaudited) - Schedule of Unaudited Quarterly Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Information [Abstract]
Total revenues	$ 89,100	$ 86,800	$ 88,500	$ 87,500	$ 66,900	$ 48,100	$ 67,300	$ 56,900	$ 351,985	$ 239,182	$ 335,519
Total operating expenses	67,500	66,100	69,000	68,500	63,900	57,500	56,900	54,000	271,117	232,282	244,411
Total operating income	21,600	20,700	19,500	19,000	3,000	(9,400)	10,400	2,900	80,868	6,900	91,108
Interest expense	5,900	5,700	5,600	5,300	4,700	900	800	800	22,438	7,198	3,227
Income before taxes	15,700	15,000	13,900	13,700	(1,700)	(10,300)	9,600	2,100	58,430	(298)	87,881
Provision for taxes	4,700	3,800	3,300	7,400	24,500	(4,400)	3,300	2,900	19,208	26,353	27,119
Net income (loss)	$ 11,000	$ 11,200	$ 10,600	$ 6,300	$ (26,200)	$ (5,900)	$ 6,300	$ (800)	$ 39,222	$ (26,651)	$ 60,762
Earnings (loss) per share:
Basic (usd per share)	$ 0.46	$ 0.45	$ 0.39	$ 0.21	$ (0.85)	$ (0.18)	$ 0.20	$ (0.02)	$ 1.46	$ (0.83)	$ 1.90
Diluted (usd per share)	$ 0.45	$ 0.43	$ 0.38	$ 0.21	$ (0.85)	$ (0.18)	$ 0.20	$ (0.02)	1.42	(0.83)	1.89
Dividends declared per share (usd per share)									$ 0.20	$ 1.4	$ 1.8