Commitments and Contingencies - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Leases
Building lease expiration period				Jun. 30, 2025
Payments for rent		$ 600,000
Future commitments and obligations under capital lease
Depreciation expense		1,561,000	$ 2,415,000	$ 4,426,000	$ 5,639,000
Furnace
Future commitments and obligations under capital lease
Capital lease term of contract			3 years
Capital lease option cancellation period				12 months
Capital lease termination month and year	2017-08
Loss recognized on termination of lease	$ 29,000
Capital lease obligation cancelled	49,000
Net book value of underlying asset	$ 79,000
Depreciation expense		2,000	$ 3,000
Sublease
Leases
Rent payment received		100,000
Future commitments and obligations under operating lease
Lease term				3 years
Future annual sublease rental income		$ 300,000		$ 300,000