Segment Information - Reconciliation of EBITDA to Net Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
EBITDA	$ 153,594	$ 167,204	$ 170,787
Less
Income tax expense (benefit)	4,780	8,271	(3,335)
Interest expense, net	29,145	24,240	23,771
Depreciation and amortization	64,250	59,567	64,974
Net income	$ 55,419	$ 75,126	$ 85,377