Restructuring Charges - Summary of Restructuring Activity (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Cost And Reserve [Line Items]
Beginning balance			$ 0	$ 1,132,000
Additions	$ 0	$ 0	2,551,000	667,000
Adjustments			0	(797,000)
Cash payments			(2,538,000)	(1,002,000)
Ending balance	13,000	0	13,000	0
Severance and Termination-Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance			0	1,132,000
Additions			2,451,000	667,000
Adjustments			0	(797,000)
Cash payments			(2,438,000)	(1,002,000)
Ending balance	13,000	0	13,000	0
Legal and Other Exit Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance			0	0
Additions			100,000	0
Adjustments			0	0
Cash payments			(100,000)	0
Ending balance	$ 0	$ 0	$ 0	$ 0