Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax [Line Items]
Increase in valuation allowance	$ 9.2	$ 0.8	$ 2.6
Federal
Income Tax [Line Items]
Net operating loss carryforwards	93.3
Research and development credit carryforwards	1.7
Federal | Minimum
Income Tax [Line Items]
Net operating loss carryforwards, expiration term	2025
Research and development credit carryforwards, expiration year	2022
Federal | Maximum
Income Tax [Line Items]
Net operating loss carryforwards, expiration term	2032
Research and development credit carryforwards, expiration year	2031
State
Income Tax [Line Items]
Net operating loss carryforwards	93.3
State | Minimum
Income Tax [Line Items]
Net operating loss carryforwards, expiration term	2015
State | Maximum
Income Tax [Line Items]
Net operating loss carryforwards, expiration term	2032
Research and development credit carryforwards	$ 1.8