Compensation Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Performance Shares [Member]
RSUs, PSUs, and Director's Shares [Abstract]
Stock-based compensation expense	$ 4,700,000	$ 2,900,000
Unrecognized stock based compensation expense	14,700,000
Common stock awards vesting multiplier, low end of range	0
Common stock awards vesting multiplier, high end of range	2
Performance period to receive awards (in years)	3
Restricted Stock Units (RSUs) [Member]
RSUs, PSUs, and Director's Shares [Abstract]
Number of Common Shares to be Received Upon Settlement	1
Stock-based compensation expense	3,000,000	1,200,000
Unrecognized stock based compensation expense	11,000,000
Employee Stock Option [Member]
Stock option activity
Stock options outstanding at the beginning of the period (in shares)	267,846
Exercised	(54,187)
Forfeited	0
Stock options outstanding at the end of the period (in shares)	213,659
Stock options vested and exercisable at the end of the period (in shares)	213,659
Weighted-Average Exercise Price
Stock options outstanding at the beginning of the period (in dollars per share)	$ 14.95
Exercised (in dollars per share)	$ 14.24
Forfeited (in dollars per share)	$ 0.00
Stock options outstanding at the end of the period (in dollars per share)	$ 15.11
Stock options vested and exercisable at the end of the period (in dollars per share)	$ 15.11
Aggregate Intrinsic Value
Outstanding at the beginning of the period	9,983,000
Exercised	2,393,000
Outstanding at the end of the period	9,424,000
Vested at the end of the period	$ 9,424,000