Commitments and Contingencies (Lease Commitments) (Details)	9 Months Ended
	Sep. 30, 2018 USD ($) lease
Lease Commitments
Number of operating leases | lease	2
Corporate headquarters
Lease Commitments
Irrevocable standby letter of credit provided to landlord	$ 785,000
Corporate headquarters | High end of range
Lease Commitments
Aggregate annual lease payments	2,500,000
Off-site back-up facility | High end of range
Lease Commitments
Aggregate annual lease payments	$ 32,000