Loans Receivable and Related Allowance for Loan Losses - Real estate rental and leasing sector (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) loan
Real Estate Rental and Leasing
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	1,281
Balance | $	$ 273,820
Lessors or Residential Buildings and Dwellings
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	930
Balance | $	$ 142,156
Lessors of Nonresidential Buildings
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	210
Balance | $	$ 99,033
Other Activities Related to Real Estate
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	47
Balance | $	$ 8,120
Lessors of Mini warehouses and Self-Storage Units
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	15
Balance | $	$ 5,860
Other General Government Support
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	17
Balance | $	$ 6,171
Lessors of Other Real Estate Property
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	13
Balance | $	$ 4,249
Real Estate Property Managers
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	11
Balance | $	$ 2,575
All Other Real Estate Rental and Leasing
Financing Receivable, Recorded Investment [Line Items]
Number of loans | loan	38
Balance | $	$ 5,656