Corporate Restructuring and Other Organizational Changes - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Position
Restructuring Cost and Reserve [Line Items]
Employee termination costs paid during the period		$ 800
Employee termination costs			$ 1,300
Number of positions eliminated | Position			30
Amounts paid during the period	$ 1,285	1,432
Restructuring charges	5,945	4,559	$ 1,045
Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance liability to be paid over the next 12 months	0	0	800
Amounts paid during the period		778	2,900
Restructuring charges			777
Facility Closures [Member]
Restructuring Cost and Reserve [Line Items]
Amounts paid during the period	1,285	654
Restructuring charges	5,945	4,559	$ 268
Facility Closures [Member] | Other Current Liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,800
Facility Closures [Member] | Other Noncurrent Liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring charges	4,100
General and Administrative Expense [Member] | Lleased Facilities in Edison, NJ; Chantilly, VA; Charlotte, SC; Parsippany, PA; and Waltham, MA [Member]
Restructuring Cost and Reserve [Line Items]
Lease termination fee	$ 2,400
General and Administrative Expense [Member] | Leased Facilities in Watford, UK; Providence, RI; Chantilly, VA; and West Hills, CA [Member]
Restructuring Cost and Reserve [Line Items]
Lease termination fee		$ 5,000