Segment Reporting - Reconciliation of Operating Profit (Loss) from Segments to Consolidated (Details) - USD ($) $ 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
Reconciliation of income from continuing operations from segments to consolidated [Abstract]
Total consolidated operating income (loss)	$ 26,994	$ 28,329	$ 21,169	$ 16,754	$ 18,110	$ 9,475	$ 8,252	$ 10,673	$ 93,246	$ 46,510	$ 22,526
Interest expense									(34,847)	(38,237)	(25,102)
Gain (loss) on investments, net									(275)	564	271
Non-operating income (loss), net									3,988	4,420	4,250
Income (loss) before income taxes									$ 62,112	$ 13,257	$ 1,945