Restructuring - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost And Reserve [Line Items]
Restructuring expenses (benefits)	$ 3,175	$ 926
Net restructuring charge	3,184	1,938	$ 36,481
Q4 2017 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses (benefits)	1,466
Net restructuring charge	$ 1,500
Restructuring liability, expected paid out period	1 year 10 months 24 days
Q3 2017 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses (benefits)	$ 918
Net restructuring charge	900
Employee severance Costs	600
Other costs	300
Q2 2017 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses (benefits)	1,242
Net restructuring charge	1,200
Employee severance Costs	1,100
Other costs	100
Q2 2015 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses (benefits)	$ (451)	926	33,800
Restructuring liability, expected paid out period	4 years 4 months 24 days
Employee severance Costs		100	10,700
Other costs	$ 400	100
Lease termination costs		$ 700	$ 23,100