Guarantees and Long Term Standby Purchase Commitments - Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 1,944
Operating Leases, Rent Expense, Net	2,000	$ 1,600	$ 1,300
Contractual Obligation, Due in Next Fiscal Year	1,965
Operating Leases, Future Minimum Payments, Due in Two Years	1,937
Contractual Obligation, Due in Second Year	1,110
Operating Leases, Future Minimum Payments, Due in Three Years	1,977
Contractual Obligation, Due in Third Year	233
Operating Leases, Future Minimum Payments, Due in Four Years	2,021
Contractual Obligation, Due in Fourth Year	0
Operating Leases, Future Minimum Payments, Due in Five Years	1,995
Contractual Obligation, Due in Fifth Year	0
Operating Leases, Future Minimum Payments, Due Thereafter	1,311
Contractual Obligation, Due after Fifth Year	0
Operating Leases, Future Minimum Payments Due	11,185
Contractual Obligation	$ 3,308