Employee Benefit Plans (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Restricted Stock Awards and Restricted Stock Units, additional information
Share-based compensation recorded	$ 8,100,000	$ 10,900,000	$ 7,800,000
Restricted Stock Awards
Restricted Stock Award and Restricted Stock Unit Activity
Nonvested at the beginning of the period (in shares)	191,578
Granted (in shares)	57,435
Vested (in shares)	(172,953)
Nonvested at the end of the period (in shares)	76,060	191,578
Weighted Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 25.01
Granted (in dollars per share)	$ 16.54
Vested (in dollars per share)	$ 24.85
Nonvested at the end of the period (in dollars per share)	$ 18.99	$ 25.01
Restricted Stock Awards and Restricted Stock Units, additional information
Unrecognized compensation expense	400,000
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	0.4
Total fair value of awards vested	4,300,000	4,500,000	7,600,000
Restricted Stock Awards | Employee
Employee benefit plans
Vesting period of awards (in years)	4 years
Restricted Stock Awards | Outside directors
Employee benefit plans
Vesting period of awards (in years)	1 year
Restricted Stock Units
Restricted Stock Award and Restricted Stock Unit Activity
Nonvested at the beginning of the period (in shares)	1,079,219
Granted (in shares)	569,000
Delivered (in shares)	(305,744)
Forfeited (in shares)	(109,300)
Nonvested at the end of the period (in shares)	1,233,175	1,079,219
Weighted Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 17.31
Granted (in dollars per share)	$ 14.57
Delivered (in dollars per share)	$ 16.39
Forfeited (in dollars per share)	$ 16.69
Nonvested at the end of the period (in dollars per share)	$ 16.33	$ 17.31
Restricted Stock Awards and Restricted Stock Units, additional information
Unrecognized compensation expense	6,000,000
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	1.6
Total fair value of awards delivered	5,000,000	2,300,000	1,400,000
Restricted Stock Units | Directors
Employee benefit plans
Vesting period of awards (in years)	1 year
Stock Purchase Plan
Restricted Stock Awards and Restricted Stock Units, additional information
Share-based compensation recorded	200,000
Employee Stock Purchase Plan
Value of shares that can be purchased as a percentage of participant's compensation	10.00%
Value of shares that can be purchased	25,000
Purchase price of shares as a percentage of the fair market value of the stock	85.00%
Number of shares reserved for issuance and purchase	350,000
Aggregate proceeds from stock plan	$ 700,000	$ 700,000	$ 400,000
Number of shares issued under the Stock Purchase Plan	50,523	54,101	39,054