Debt Obligations (Details) (USD $)
In Millions, unless otherwise specified

3 Months Ended

Sep. 30, 2012

Dec. 31, 2011

Dec. 13, 2006

Convertible Senior Subordinated Notes [Member]

Debt Instrument [Line Items]

Face amount

$ 143.8

Interest rate (in hundredths)

2.4375%

Maturity date

2027

Terms of conversion feature

Under certain circumstances, the convertible notes are convertible into cash, or a combination of cash and common stock at the company’s election, based on an initial conversion rate of 40.8513 shares of the company’s common stock per $1,000 in principal amount of the convertible notes (equivalent to an initial conversion price of approximately $24.48 per share).  At any time on or after January 21, 2014, the convertible notes are subject to redemption at the option of the company, in whole or in part, for cash equal to 100% of the principal amount of the convertible notes, plus unpaid interest, if any, accrued to the redemption date.  Holders of the convertible notes may require the company to repurchase the convertible notes, in whole or in part, on January 15, 2014, January 15, 2017 or January 15, 2022, for cash equal to 100% of the principal amount of the convertible notes, plus any unpaid interest, if any, accrued to the redemption date.  In addition, holders of the convertible notes may require the company to repurchase the convertible notes, in whole or in part, for cash equal to 100% of the principal amount of the convertible notes, plus any unpaid interest, if any, accrued to the redemption date, if a “fundamental change” occurs prior to maturity of the convertible notes.

Fair value of debt

144.5

145.2

Credit Facility [Member]

Debt Instrument [Line Items]

Term of credit facility (in years)

5Y

Maximum borrowing capacity

300

Expiration date of credit facility

2016-06-07

Capacity for the issuance of standby letters of credit

125

Maximum increase in borrowing capacity

150

Interest rate description

Loans under the Credit Facility bear interest at LIBOR plus an applicable margin ranging from 1.75% to 2.50%, with the applicable margin varying according to the company's total leverage ratio, or, at the election of the company, at a prime base rate plus 0.75% to 1.50%. Letters of credit issued under the Credit Facility accrue fees at a rate equal to the applicable margin for LIBOR loans. In addition, the company is required to pay a quarterly commitment fee for the unused portion of the Credit Facility, if any, at a rate ranging from 0.30% to 0.50%.

Variable rate basis of loans under the credit facility

LIBOR

Basis spread on variable rate, minimum (in hundredths)

1.75%

Basis spread on variable rate, maximum (in hundredths)

2.50%

Basis spread on prime base rate, at the company's election, minimum (in hundredths)

0.75%

Basis spread on prime base rate, at the company's election, maximum (in hundredths)

1.50%

Unused capacity, commitment fee description

In addition, the company is required to pay a quarterly commitment fee for the unused portion of the Credit Facility, if any, at a rate ranging from 0.30% to 0.50%.

Commitment fee for the unused portion of the credit facility, minimum (in hundredths)

0.30%

Commitment fee for the unused portion of the credit facility, maximum (in hundredths)

0.50%

Letters of credit issued

15.4

Amount available for borrowings

$ 284.6