Borrowings (Details 2) (USD $)	9 Months Ended	3 Months Ended
	Sep. 30, 2012 Credit Agreement	Sep. 30, 2012 Master Lease Agreement	Aug. 10, 2012 Master Lease Agreement
Credit Agreement
Credit facility initial term	3 years
Current borrowing capacity	$ 150,000,000		$ 25,000,000
Master lease facility, amount available for funding leasehold improvements			14,000,000
Maximum period of expenditures reimbursed made during interim funding period		90 days
Interest, margin over base rate (as a percent)		2.25%
Interest, base rate		30-day LIBOR
Term of capital lease		48 months
Ending purchase price of underlying equipment		$ 1,000
Variable rate basis on captial lease obligation		4-year LIBOR
Interest, margin over base rate (as a percent)		2.25%