Notes Payable - Schedule of Information Related to Lines of Credit (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Maximum amount outstanding	$ 239,820	$ 295,588
Average amount outstanding	$ 214,446	$ 236,860
Weighted average interest rate, during the period	2.19%	2.35%
Prime interest rate, end of period	3.75%	3.50%