Restructuring - Summary of Significant Restructuring Plan Activity Related To Employees And Other Charges (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost And Reserve [Line Items]
Restructuring liability, Beginning balance	$ 19,388	$ 26,406
Restructuring expense and adjustments	3,175	926
Cash payments	(8,033)	(7,944)
Restructuring liability, Ending balance	14,530	19,388	$ 26,406
Cumulative costs to date, as of December 31, 2017	37,950
Total costs expected to be incurred, as of December 31, 2017	39,106
Q4 2017 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense and adjustments	1,466
Cash payments	(1,095)
Restructuring liability, Ending balance	371
Cumulative costs to date, as of December 31, 2017	1,466
Total costs expected to be incurred, as of December 31, 2017	2,610
Q3 2017 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense and adjustments	918
Cash payments	(911)
Restructuring liability, Ending balance	7
Cumulative costs to date, as of December 31, 2017	918
Total costs expected to be incurred, as of December 31, 2017	920
Q2 2017 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expense and adjustments	1,242
Cash payments	(1,242)
Cumulative costs to date, as of December 31, 2017	1,242
Total costs expected to be incurred, as of December 31, 2017	1,252
Q2 2015 Restructuring Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring liability, Beginning balance	19,388	26,406
Restructuring expense and adjustments	(451)	926	33,800
Cash payments	(4,785)	(7,944)
Restructuring liability, Ending balance	14,152	$ 19,388	$ 26,406
Cumulative costs to date, as of December 31, 2017	34,324
Total costs expected to be incurred, as of December 31, 2017	$ 34,324