Summary of Significant Accounting Policies - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Interest paid	$ 11,573	$ 7,307	$ 6,877
Taxes paid	316	3,125	9,778
Non-cash activities:
Purchases of property and equipment not paid	$ 824	$ 2,104	$ 3,241