Financial Guarantee Liability - Summary of Estimated Liability under Guarantee Liability (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Guarantees [Abstract]
Beginning Balance	$ (413)	$ (288)
Increase to provision		(125)
Reversal of provision	347
Ending Balance	$ (66)	$ (413)