Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies Disclosure [Line Items]
Minimum term of non-cancelable operating leases	1 year
Expiration of non-cancelable operating leases maximum year	2019
Operating lease, rent expense	$ 0.6	$ 0.7	$ 0.9
Financing for leasehold improvement			1.1
Outstanding liability related to leasehold improvements	0.8
Leasehold Improvements reflected in Accrued liabilities	0.1
Leasehold Improvements reflected in Other non-current liabilities	0.7
Purchase commitment, paid	7.2	3.6	0.9
Future minimum purchase commitment 2013	2.5
Future minimum purchase commitment 2014	0.1
Future minimum purchase commitment 2015	$ 0.1
Concord Lease
Commitments and Contingencies Disclosure [Line Items]
Early termination of non-cancelable operating leases minimum period	2015-01