Balance Sheet Account Detail - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Schedule Of Investments In Marketable Securities [Line Items]
Securities in continuous unrealized loss position, period	longer than one year.
Depreciation expense	$ 0.1	$ 0.2
Intangible asset amortization expense	$ 6.9
Other Intangible Assets [Member]
Schedule Of Investments In Marketable Securities [Line Items]
Intangible asset amortization expense		$ 5.8