Schedule IV - Changes in Carrying Amount of Mortgage Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Mortgage Loans On Real Estate [Abstract]
Beginning balance	$ 32,366	$ 32,737	$ 48,455
New mortgage loans	4,287	1,505	1,814
Loan repayments	(2,368)	(1,227)	(16,714)
Collection of principal	(766)	(649)	(818)
Ending balance	$ 33,519	$ 32,366	$ 32,737