Notes Payable - Schedule of Information Related to Lines of Credit (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Maximum amount outstanding	$ 228,500	$ 215,732
Average amount outstanding	$ 204,534	$ 199,499
Weighted average interest rate, during the period	3.36%	2.64%
Prime interest rate, end of period	5.50%	4.50%