Commitments and Contingencies - Other Information Related to Leases (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Cash paid for amounts included in the measurement of lease liabilities, operating cash flows from operating leases	$ 2,655	$ 2,449	$ 5,255	$ 4,972
Cash paid for amounts included in the measurement of lease liabilities, operating cash flows from finance leases	95	155	204	334
Cash paid for amounts included in the measurement of lease liabilities, financing cash flows from finance leases	2,013	2,564	4,172	5,366
Right-of-use assets obtained in exchange for lease obligations, operating leases	(1,026)	506	91	3,866
Right-of-use assets obtained in exchange for new finance lease liabilities	$ 4,043	$ 18	$ 4,142	$ 102
Weighted average remaining lease term (years), operating leases	3 years 8 months 12 days	4 years 3 months 10 days	3 years 8 months 12 days	4 years 3 months 18 days
Weighted average remaining lease term (years), finance leases	2 years 2 months 1 day	2 years 4 months 24 days	2 years 2 months 1 day	2 years 4 months 24 days
Weighted average discount rate, operating leases	4.10%	4.00%	4.10%	4.00%
Weighted average discount rate, finance leases	3.70%	3.00%	3.70%	3.00%