Geographical Information - Revenue by Geographical Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 861,390	$ 741,420	$ 764,717
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	567,315	507,473	506,268
All Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 294,075	$ 233,947	$ 258,449