Financial Guarantee Liability - Summary of Changes on Estimated Liability Under Guarantee Liability (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Guarantees [Abstract]
Beginning Balance	$ (54)	$ (413)
Reversal of provision		359
Increase to provision	(7)
Ending Balance	$ (61)	$ (54)