Credit Facilities (Additional Information) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jan. 31, 2012	Dec. 31, 2011
Line of Credit Facility [Line Items]
Line of credit		$ 25.0	$ 5.0
Annual interest rate	1-month LIBOR Daily Floating Rate plus 1.85%
Spread over LIBOR	1.85%
Unused commitment fees	0.25%
Loan agreement expiration date	Feb. 14, 2013
Outstanding borrowing under line of credit	0			0
Outstanding letters of credit	$ 2.6			$ 2.6