Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclsoure [Line Items]
Net charge related to new accounting requirements for share-based compensation	$ 1,500
Revaluation of deferred tax assets and liabilities, resulting in a net charge	15,400
Valuation allowance for operating loss carryforwards and other deferred tax assets	3,400
Foreign loss carryforwards	37,400
Deferred tax asset, net of valuation allowance	42,345	$ 62,108
Income taxes receivable	$ 2,000	$ 1,400
U.S. statutory tax rate	35.00%	35.00%	35.00%
Carryforward limitation, 4 to 6 years
Income Tax Disclsoure [Line Items]
Foreign loss carryforwards	$ 600
Foreign Tax Authority | Her Majesty's Revenue and Customs (HMRC)
Income Tax Disclsoure [Line Items]
Deferred tax asset, net of valuation allowance	$ 2,100
Minimum
Income Tax Disclsoure [Line Items]
Carryforward period	8 years
Minimum | Carryforward limitation, 4 to 6 years
Income Tax Disclsoure [Line Items]
Carryforward period	4 years
Maximum | Carryforward limitation, 4 to 6 years
Income Tax Disclsoure [Line Items]
Carryforward period	6 years