Recently Issued Accounting Standards - Contract Balances (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Contract Assets [Roll Forward]
Beginning balance January 1, 2018	$ 14,611
Ending balance March 31, 2018	14,004
Increase (decrease) in accounts receivable	(607)
Contract Liabilities, Current [Roll Forward]
Beginning balance January 1, 2018	860
Ending balance March 31, 2018	860
Increase (decrease) in contract liability (current)	0
Contract Liabilities, Noncurrent [Roll Forward]
Beginning balance January 1, 2018	1,766
Ending balance March 31, 2018	1,458
Increase (decrease) in contract liability (long-term)	$ (308)