Information on Long-Lived Assets and Net Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Property and equipment, net of accumulated depreciation	$ 61,856	$ 74,760
UNITED STATES
Segment Reporting Information [Line Items]
Property and equipment, net of accumulated depreciation	39,584	47,107
Net assets	709,634	660,396
UNITED KINGDOM
Segment Reporting Information [Line Items]
Property and equipment, net of accumulated depreciation	15,312	20,335
Net assets	193,276	210,801
All Other Foreign Countries
Segment Reporting Information [Line Items]
Property and equipment, net of accumulated depreciation	6,960	7,318
Net assets	$ 304,448	$ 276,406