Notes Payable Convertible Senior Notes and Line of Credit - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Oct. 31, 2009 Convertible Notes Payable	Dec. 31, 2012 Convertible Notes Payable	Jan. 31, 2013 Conversion of Debt Convertible Notes Payable
Debt Instrument [Line Items]
Principal payments on notes in 2013	$ 2,000,000
Principal payments on notes in 2014	2,000,000
Principal payments on notes in 2015	1,900,000
Principal payments on notes in 2016	600,000
Convertible senior notes, aggregate principal amount				65,000,000
Convertible senior notes, interest rate				6.00%
Convertible senior notes, maturity date				2014
Convertible senior notes, carrying amount						20,700,000
Convertible senior notes, conversion rate of shares issued					77.6398	1,691,074
Convertible senior notes, conversion rate of principal amount		1,299,000			1,000
Convertible senior notes, conversion price per share					$ 12.88
Convertible senior notes, conversion price dividend adjustment					$ 0.10
Notes payable, debt issuance cost	3,300,000
Notes payable, amortization of debt issuance costs	600,000	500,000	500,000
Notes payable, interest expense	4,200,000	4,200,000	4,200,000
Bank line of credit facility amount	$ 10,000,000
Bank line of credit facility, expiration date	2013-06