Commitments - Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating lease obligations
Operating lease obligation, Total	$ 2,326
2018	502
2019	674
2020	395
2021	117
2022	120
Beyond	518
Credit facility
Total debt	48,750
2018	5,000
2019	5,000
2020	38,750
2021	0
2022	0
Beyond	0
Purchase obligations
Purchase Obligation, Total	80,369
2018	80,369
2019	0
2020	0
2021	0
2022	0
Beyond	0
Total obligations
Total obligations	131,445
2018	85,871
2019	5,674
2020	39,145
2021	117
2022	120
Beyond	518
Operating leases rent expense	$ 153	$ 162