Notes Receivable - Loans Receivable on Real Estate (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Receivables [Abstract]
Balance at January 1	$ 49,488	$ 41,988
Additions:
New mortgage loans	0	4,611
Interest	523	17
Accretion of discount	269	511
Deductions:
Collections of principal and interest	(30,701)	(257)
Balance at June 30	$ 19,579	$ 46,870