Mortgage Loans - Additional Information (Detail)	6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) loan	Jun. 30, 2018 loan	Dec. 31, 2018 USD ($) loan
Financing Receivable, Modifications [Line Items]
Number of mortgage loan foreclosed | loan	1		4
Mortgage loans foreclosed | $	$ 7,363,000		$ 22,608,000
Number of loans in foreclosure process | loan	1		1
Mortgage loans foreclosure process | $	$ 8,644,000		$ 7,363,000
Number of mortgage loans sold | loan	0		0
Unamortized discounts | $	$ 0		$ 0
Unamortized origination fees, mortgage loans | $	$ 29,356,000		$ 31,586,000
Number of Loans | loan	7	0
Commitment to lend additional funds to debtors with modified loans as TDRs | $	$ 4,042,000
Retail
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	2	0