Operating Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) installment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Future Minimum Lease Payments Under Noncancelable Operating Leases [Line Items]
Description of lease | installment	12
Rent expense	$ 3,900	$ 3,900	$ 3,800
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments Due	24,009
2018	4,243
2019	4,090
2020	4,041
2021	3,744
2022	1,733
Thereafter	$ 6,158
Office Lease
Future Minimum Lease Payments Under Noncancelable Operating Leases [Line Items]
Lease expiration year	2023
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments Due	$ 8,354
2018	2,221
2019	2,062
2020	2,011
2021	1,711
2022	200
Thereafter	149
Ground Lease
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments Due	15,655
2018	2,022
2019	2,028
2020	2,030
2021	2,033
2022	1,533
Thereafter	$ 6,009
Minimum | Ground Lease
Future Minimum Lease Payments Under Noncancelable Operating Leases [Line Items]
Lease expiration year	2018
Maximum | Ground Lease
Future Minimum Lease Payments Under Noncancelable Operating Leases [Line Items]
Lease expiration year	2054