Line of Credit - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2014
Line of Credit Facility [Line Items]
Repayment of line of credit		$ 125,000,000
Interest expense		36,781	$ 7,073
Secured Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit maximum amount	$ 150,800,000
Line of credit, collateral amount held by the lender	$ 150,800,000
Variable interest rate	2.991%
Line of credit borrowed amount	$ 125,000,000
Repayment of line of credit	$ 125,000,000
Description of variable rate basis	LIBOR plus 2.991%
Interest expense		$ 36,781