Stock-Based Compensation Plans (Details 2) (USD $)	12 Months Ended
Dec. 31, 2011 Y	Dec. 31, 2010 Y	Dec. 31, 2009
Stock option activity
Number of shares, Beginning balance	4,403,562	5,166,558	5,287,175
Number of shares, Granted	340,771	8,239	140,239
Number of shares, Cancelled	(211,323)	(12,575)	(199,932)
Number of shares, Exercised	(1,605,273)	(758,660)	(60,924)
Number of shares, Ending balance	2,927,737	4,403,562	5,166,558
Number of shares, Exercisable	2,679,941
Weighted average exercise price, Beginning balance	$ 9.09	$ 9.10	$ 9.17
Weighted average exercise price, Granted	$ 21.60	$ 14.10	$ 9.66
Weighted average exercise price, Cancelled	$ 16.16	$ 13.85	$ 11.07
Weighted average exercise price, Exercised	$ 10.21	$ 9.17	$ 9.54
Weighted average exercise price, Ending balance	$ 9.42	$ 9.09	$ 9.10
Weighted average exercise price, Exercisable	$ 8.36
Remaining contractual term, Balance	8.1	4.4
Remaining contractual term, Exercisable	8.1
Intrinsic value, Exercised	$ 24,192
Intrinsic value, Ending balance	60,589
Intrinsic value, Exercisable	$ 58,287

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance sheet date.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated during the reporting period due to noncompliance with plan terms during the reporting period.

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