Commitments and Contingencies - Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
2017	$ 2,242
2018	1,965
2019	1,146
2020	662
2021	221
Total future minimum lease commitments	6,236
Rent expense	$ 2,100	$ 2,300	$ 2,700