Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 176,490	$ 165,813
Research and development credit carryforwards	31,777	35,131
Capitalized research and development	22,575	17,916
Deferred compensation	8,242	5,908
Other	3,184	3,911
Total deferred tax assets	242,268	228,679
Valuation allowance	(238,443)	(224,854)
Net deferred tax assets	3,825	3,825
Deferred tax liabilities:
Unrealized gain on investments	3,825	3,825
Amortization of goodwill	150	122
Total deferred tax liabilities	$ 3,975	$ 3,947