Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements of Changes in Stockholders' Equity
Issuance of common stock for stock options, shares	111,792	125,268	214,445
Issuance of common stock for restricted share awards, shares	787,399	317,489	183,513
Issuance of common stock for employee stock unit awards, shares	288,917	311,106	168,248
Issuance of common stock for stock options, restricted share awards and employee stock unit awards, tax benefit shortfall (in dollars)	$ 3.3	$ 2.2	$ 1.5
Issuance of common stock for the employee stock purchase plan, shares	108,621	108,454	99,847
Purchase of common stock for treasury, shares	2,974,200	3,151,828
Shares withheld for net settlements of share-based awards, shares	369,099	235,075	119,801