Contract Assets and Contract Liabilities - Current and Long-term Contract Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract with Customer, Asset, Gross	$ 9,397	$ 6,694
Contract with Customer, Liability, Current	(3,923)	$ (2,252)
within 12 to 24 months
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract liabilities	4,509
greater than 24 months
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract liabilities	$ 965