Lease Agreements - Future Minimum Rental Payments for Operating and Capital Leases (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Capital Leases
Capital leases minimum payments for 2018	$ 118
Capital leases minimum payments for 2019	117
Capital leases minimum payments for 2020	54
Capital leases minimum payments for 2021	0
Capital leases minimum payments for 2022	0
Capital leases minimum payments for later years	0
Capital leases minimum payments total	289
Operating Leases
Operating leases minimum payments for 2018	7,970
Operating leases minimum payments for 2019	5,848
Operating leases minimum payments for 2020	4,878
Operating leases minimum payments for 2021	4,511
Operating leases minimum payments for 2022	4,643
Operating leases minimum payments for later years	7,255
Operating leases minimum payments total	35,105
Built-to-Suit Lease
Built-to-suit leases minimum payments for 2018	897
Built-to-suit leases minimum payments for 2019	915
Built-to-suit leases minimum payments for 2020	933
Built-to-suit leases minimum payments for 2021	952
Built-to-suit leases minimum payments for 2022	971
Built-to-suit leases minimum payments for later years	8,451
Built-to-suit leases minimum payments total	$ 13,119