Revenue Recognition - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Jan. 02, 2018
Contract Assets and Liabilities
Contract asset, current	$ 1,309	$ 1,309	$ 1,176
Change in contract asset - current		133
% of change in contract asset - current	11.00%
Contract asset, noncurrent	$ 498	498	453
Change in contract Asset – noncurrent		45
% of change in contract Asset – noncurrent	10.00%
Contract liabilities	$ (9,827)	(9,827)	(9,912)
Change in contract liabilities		85
% of change in contract liabilities	(1.00%)
Net contract liability	$ (8,020)	(8,020)	$ (8,283)
Change in net contract liability		$ 263
% of change in net contract liability	(3.00%)
Revenue recognized related to contract liability	$ 9,600
Amortization of contract assets	300
Revenue recognized in the period related to performance obligations that were satisfied or partially satisfied in previous periods	$ 0