Description of Business and Significant Accounting Policies - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Impairment of goodwill	$ 0	$ 0
ASU No. 2016-09 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Unrecognized excess tax benefits of deferred tax assets offset by valuation allowance				$ 6,219,000
ASU No. 2016-09 [Member] | Retained Earnings [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Adjustment to opening retained earnings			$ 25,000