Changes in Mortgage Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Mortgage Loans On Real Estate [Abstract]
Balance at beginning of period	$ 120,130	$ 209,566	$ 297,451
Additions during period:
Interest	12,150	18,285	20,807
Deductions during period:
Provision for loan loss reserve	(19,393)	(15,544)	(11,422)
Collections of principal and interest	(112,887)	(92,177)	(97,270)
Balance at close of period	$ 0	$ 120,130	$ 209,566