Line Of Credit (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility	$ 40.0
Expiration date of credit facility	July 28, 2013
Outstanding balance under credit facility	18.2	21.2
Interest rate of credit facility	2.00%	2.00%
Unused and available portion of credit facility	21.8	18.8
Eurocurrency Loans [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility	10.0
Debt instrument rate, minimum	1.75%
Debt instrument rate, maximum	2.25%
Committed Loans [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility	30.0
Letters Of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility	$ 7.5
LIBOR [Member]
Line of Credit Facility [Line Items]
Debt instrument rate, minimum	1.75%
Debt instrument rate, maximum	2.25%
Federal Funds Rate [Member]
Line of Credit Facility [Line Items]
Debt instrument rate, minimum	0.25%
Debt instrument rate, maximum	0.75%
Federal Funds Rate [Member] | Committed Loans [Member]
Line of Credit Facility [Line Items]
Basis spread on federal funds rate	0.50%