Leases - Cost and Accumulated Depreciation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Future minimum rental payments under noncancelable leases
Remainder of 2019	$ 7,040
2020	8,691
2021	7,984
2022	5,125
2023	2,632
Thereafter	34,638
Office space leased in headquarters office and to third party lessees
Cost	288,700	$ 289,200
Accumulated depreciation	$ 135,400	$ 133,700
Future minimum rental income from related parties	not material
Related parties associated with its branch premises
Lease payments to related parties	$ 200
Future minimum rental payments under noncancelable leases
Remainder of 2019	200
2020	300
2021	300
2022	200
2023	200
Thereafter	$ 7,500