Loans Receivable - Activity in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				$ 11,308				$ 10,033	$ 11,308	$ 10,033
Provision charged to operating expense	$ 921	$ 1,071	$ 677	121	$ 500	$ 495	$ 630	515	2,791	2,140
Recoveries									34	231
Balance at end of year	13,301				11,308				13,301	11,308
Unfunded Lines of Credit
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				1,053				901	1,053	901
Provision charged to operating expense									173	152
Recoveries									0	0
Charge-offs									0	0
Balance at end of year	1,226				1,053				1,226	1,053
Mortgage Loans Sold
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of year				$ 501				$ 457	501	457
Provision charged to operating expense									184	106
Recoveries									0	0
Charge-offs									(109)	(62)
Balance at end of year	$ 576				$ 501				$ 576	$ 501