Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit)	$ 8,000
Tax cuts and jobs act of 2017, change in tax rate, deferred tax assets and liabilities, impact on valuation allowance	400
Tax expense resulting from share-based compensation tax benefits	1,800	$ 1,400	$ 6,900
Deferred tax assets, state NOLs	4,500
Deferred tax assets, federal NOLs	2,200
Research and development tax credit studies	15,200
Liability for unrecognized tax benefits		4,100
Threshold to favorably impact effective tax rate	4,200
Unrecognized tax benefits, accrued interest	100	$ 100
ARIZONA | 2019
Income Tax Contingency [Line Items]
Minimum tax credit carryover	1,200
AUSTRALIA
Income Tax Contingency [Line Items]
Deferred tax assets, foreign NOLs	2,200
UNITED KINGDOM
Income Tax Contingency [Line Items]
Deferred tax assets, foreign NOLs	10,300
CANADA
Income Tax Contingency [Line Items]
Deferred tax assets, foreign NOLs	1,600
GERMANY
Income Tax Contingency [Line Items]
Deferred tax assets, foreign NOLs	300
Federal
Income Tax Contingency [Line Items]
Federal research and development credit carry forwards	136
State
Income Tax Contingency [Line Items]
Liability for unrecognized tax benefits	100
State | ARIZONA
Income Tax Contingency [Line Items]
State research and development credit carry forwards	$ 7,300