Income Taxes - Reconciliation of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Net operating losses	$ 2,647	$ 4,182
Deferred revenue	2,421	8,434
Accrued expenses	1,357	700
Deferred rent	322	201
Credit carryforwards	2,342	1,357
Incentive from lessor	46	1,023
Facility exit obligation	1,102	0
Depreciation	304	0
Stock-based compensation	7,474	1,333
Other	1,017	1,130
Total deferred tax assets	19,032	18,360
Less valuation allowance	(13,270)	(13,829)
Deferred tax assets net	5,762	4,531
Deferred tax liabilities:
Depreciation	(5,016)	(4,531)
Net deferred tax assets	$ 746	$ 0