Significant Accounting Policies (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Accounting Policies [Abstract]
Goodwill impairment loss			$ 0		$ 0
Impairment of intangible assets			0		0
Impairment of cost method investments			0		$ 0
Interest paid	$ 0	$ 0	0	$ 0
Income taxes paid	400,000	$ 0	400,000	$ 0
Capital expenditures incurred but not yet paid (less than)	100,000		100,000
Proceeds from escrow releases	$ 11,300,000		$ 11,300,000