Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Benefit for income taxes	$ 1,466	$ 464	$ 1,412	$ 635
U.S. federal statutory tax rate			35.00%
Tax on currency transactions	$ 2,000	$ 300	$ 2,000	$ 900
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income tax asset					$ 2,700
Excess tax benefit					$ 2,700