Leases - Third Party Leases, Cost and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Lease payments to related parties	$ 300
Future minimum rental payments under noncancelable leases
2020	8,776
2021	8,084
2022	5,453
2023	2,964
2024	2,721
Thereafter	32,227
Office space leased in headquarters office and to third party lessees
Cost	547,071	$ 522,813
Accumulated Depreciation	$ 230,186	217,817
Terms of such leases
Lessor, renewal options included	true
Future minimum rental income from related parties
2020	$ 6,164
2021	6,152
2022	4,431
2023	3,506
2024	2,680
Thereafter	6,511
Third party lessees
Office space leased in headquarters office and to third party lessees
Cost	$ 288,800	289,200
Terms of such leases
Lessor, Operating Lease, Renewal Term	10 years
Operating lease income related to lease payments
Operating lease income	$ 5,900
Lease income related to variable lease payments	5,300
Rental income paid by related parties	400
Future minimum rental income from related parties
2020	400
2021	400
2022	400
2023	400
2024	400
Thereafter	800
Buildings
Office space leased in headquarters office and to third party lessees
Cost	289,271	280,853
Accumulated Depreciation	141,300	$ 133,700
Related parties associated with its branch premises
Future minimum rental payments under noncancelable leases
2020	300
2021	300
2022	200
2023	200
2024	200
Thereafter	$ 7,300