Mortgage Loans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Receivables [Abstract]
Number of mortgage loan foreclosed | loan	2	4
Mortgage loans foreclosed	$ 16,008,000	$ 22,608,000
Number of loans in foreclosure process | loan	2	1
Mortgage loans foreclosure process	$ 13,345,000	$ 7,363,000
Unamortized discounts	0	0
Unamortized origination fees, mortgage loans	$ 29,294,000	$ 31,586,000
Number of Loans | loan	3	3
Commitment to lend additional funds to debtors with modified loans as TDRs	$ 0	$ 0