Compensation Plans (Details) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 25, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
RSUs, PSUs, and Director's Shares [Abstract]
Stock-based compensation expense				$ 18,068,000	$ 12,372,000
Aggregate Intrinsic Value
Document Period End Date				Jun. 30, 2013
Cash Bonus Plan [Member]
Compensation plans
Accrued Cash Bonus Plan Expense		5,300,000	4,600,000	10,900,000	9,300,000
Performance Shares [Member]
Compensation plans
Shares Paid for Tax Withholding for Share Based Compensation	200,050
RSUs, PSUs, and Director's Shares [Abstract]
Stock-based compensation expense		5,000,000	5,200,000	9,700,000	8,100,000
Unrecognized stock based compensation expense		9,800,000		9,800,000
Common stock awards vesting multiplier, low end of range		0		0
Common stock awards vesting multiplier, high end of range		2		2
Performance period to receive awards (in years)				3
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	274,831
Multiplier Applied to PSU Awards at Settlement	1.725
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period, Net of Shares Withheld for Tax	387,461
Restricted Stock Units (RSUs) [Member]
Compensation plans
Shares Paid for Tax Withholding for Share Based Compensation	66,112
RSUs, PSUs, and Director's Shares [Abstract]
Number of Common Shares to be Received Upon Settlement				1
Stock-based compensation expense		3,300,000	1,400,000	6,300,000	2,600,000
Unrecognized stock based compensation expense		7,700,000		7,700,000
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	327,605
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	201,501
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period, Net of Shares Withheld for Tax	135,389
Employee Stock Option [Member]
Stock option activity
Stock options outstanding at the beginning of the year (in shares)				267,846
Exercised				(121,318)
Forfeited				0
Stock options vested and exercisable at the end of the period (in shares)		146,528		146,528
Weighted-Average Exercise Price
Stock options outstanding at the beginning of the period (in dollars per share)				$ 14.95
Exercised (in dollars per share)				$ 13.85
Forfeited (in dollars per share)				$ 0.00
Stock options outstanding at the end of the period (in dollars per share)		$ 15.84		$ 15.84
Stock options vested and exercisable at the end of the period (in dollars per share)		$ 15.84		$ 15.84
Aggregate Intrinsic Value
Outstanding at the beginning of the period				9,983,000
Exercised				5,638,000
Outstanding at the end of the period		6,378,000		6,378,000
Vested at the end of the period		6,378,000		6,378,000
Shares Issued to the Board of Directors [Member]
Compensation plans
Stock Issued During Period, Shares, Share-based Compensation, Gross				28,169	26,500
RSUs, PSUs, and Director's Shares [Abstract]
Stock-based compensation expense				1,400,000	1,100,000
Employee Stock [Member]
Compensation plans
ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentOfOfferingDatePricePaid				85.00%
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate		15.00%		15.00%
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription		$ 25,000		$ 25,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		1,300,000		1,300,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans		44,437	37,124