Lease Financing Obligation - Additional Information (Detail) - San Diego Office Complex $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015 USD ($) Building
Schedule of Finance Lease Obligations [Line Items]
Land and buildings, net book value		$ 71.0
Proceeds from sale of assets		$ 85.5
Number of building in sale and leaseback arrangement | Building		2
Loss from sale of land and building		$ (5.3)
Building One
Schedule of Finance Lease Obligations [Line Items]
Leasing back term		10 years
Leasing back term, description	The Company determined that the sale-leaseback of Building 1 did not qualify for sale-leaseback accounting due to continuing involvement that will exist for the 10-year lease term. Accordingly, the carrying amount of Building 1 will remain on the Company's balance sheet and will be depreciated over its remaining useful life with the proceeds reflected as a financing obligation.
Building Two | Maximum
Schedule of Finance Lease Obligations [Line Items]
Leasing back term		1 year