Schedule IV - Changes in Mortgage Loans Excluding Unamortized Loan Issue Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Mortgage Loans On Real Estate [Abstract]
Balance at beginning of year	$ 1,213,283	$ 1,778,264	$ 1,060,336
New mortgage loans and additional advances on existing loans	61,712	50,783	717,928
Mortgage loans on real estate including additions during year	1,274,995	1,829,047	1,778,264
Collection of principal		(615,764)
Deductions during year		(615,764)
Balance at end of year	$ 1,274,995	$ 1,213,283	$ 1,778,264