Borrowings (Convertible Senior Notes Due 2013) (Details) (USD $)	0 Months Ended	12 Months Ended
	Mar. 07, 2008	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Debt Instrument [Line Items]
Difference between proceeds from issuance of debt and fair value of liability, deferred taxes		$ 6,900,000
Convertible Senior Notes Due 2013 [Member]
Debt Instrument [Line Items]
Debt instrument issuance amount	310,000,000
Interest rate percentage on issued debt	3.00%
Convertible senior notes discount rate		4.50%
Year of maturity of debt	2013
Expected life for accretion of discount rate, start date		March 7, 2008
Expected life for accretion of discount rate, end date		March 15, 2013
Converted share	14.7113
Principal amount of initial conversion rate	1,000
Accrued interest		2,700,000
Pre tax non-cash interest expense recognized in consolidated statement of operations		4,300,000	4,100,000	3,900,000
Annual pre-tax increase in non-cash interest expense		4,300,000
Accumulated amortization related to debt discount		15,400,000	11,100,000
Debt Instrument, Liability Components [Member] | Convertible Senior Notes Due 2013 [Member]
Debt Instrument [Line Items]
Debt instrument issuance amount		290,300,000
Debt Instrument, Equity Components [Member]
Debt Instrument [Line Items]
Difference between proceeds from issuance of debt and fair value of liability, net of deferred taxes		12,800,000
Debt Instrument, Equity Components [Member] | Convertible Senior Notes Due 2013 [Member]
Debt Instrument [Line Items]
Debt instrument issuance amount		$ 19,700,000