Intangible Assets and Goodwill - Schedule of Goodwill (Detail) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Beginning balance				$ 72,683,000	$ 35,633,000	$ 72,683,000
Goodwill impairment	$ 0	$ (1,650,000)	$ (35,400,000)	$ 0	0	(37,050,000)	$ 0
Other changes in goodwill					0
Ending balance	$ 35,633,000				$ 35,633,000	$ 35,633,000	$ 72,683,000