Mortgage Loans - Additional Information (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) loan	Sep. 30, 2018 loan	Dec. 31, 2018 USD ($) loan
Financing Receivable, Modifications [Line Items]
Number of mortgage loan foreclosed	2		4
Mortgage loans foreclosed | $	$ 16,008,000		$ 22,608,000
Number of loans in foreclosure process	0		1
Mortgage loans foreclosure process | $			$ 7,363,000
Number of mortgage loans sold	0		0
Unamortized discounts | $	$ 0		$ 0
Unamortized origination fees, mortgage loans | $	$ 28,335,000		$ 31,586,000
Number of Loans	3	1
Retail
Financing Receivable, Modifications [Line Items]
Number of Loans	2	0