Stock-Based Incentive Plans (Details) (USD $)	6 Months Ended		12 Months Ended	0 Months Ended	6 Months Ended		0 Months Ended
	Jun. 30, 2013 plan	Jun. 30, 2012	Dec. 31, 2012	Feb. 06, 2013 Restricted Stock Units	Jun. 30, 2013 Restricted Stock Units	Jun. 30, 2012 Restricted Stock Units	Feb. 06, 2013 Non Employee Directors Restricted Stock Units
Stock-Based Incentive Plans
Number of stock-based incentive plans	1
Number of stock option plans superseded	2
Restricted stock unit activity
Outstanding at the beginning of the period (in shares)					264,000
Awarded (in shares)				359,371	359,000		9,975
Vested (in shares)					(169,000)
Forfeited (in shares)					(1,000)
Outstanding at the end of the period (in shares)					453,000
Outstanding and expected to vest at the end of the period (in shares)					442,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 31.58				$ 33.23
Awarded (in dollars per share)				$ 31.96
Forfeited (in dollars per share)	$ 40.65
Outstanding at the end of the period (in dollars per share)	$ 29.45		$ 31.58		$ 32.45
Outstanding and expected to vest at the end of the period (in dollars per share)					$ 32.45
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 717,000				$ 13,339,000
Outstanding and expected to vest at end of the period (in dollars)	713,000				12,993,000
Closing price per share (in dollars per share)					$ 29.42
Total intrinsic value of awards vested (in dollars)					5,500,000	3,100,000
Non-Qualified Stock Options activity
Outstanding at the beginning of the period (in shares)	1,907,000
Exercised (in shares)	(30,000)
Forfeited (in shares)	(374,000)
Outstanding at the end of the period (in shares)	1,503,000		1,907,000
Outstanding and expected to vest at the end of the period (in shares)	1,478,000
Exercisable at the end of the period (in shares)	890,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 31.58				$ 33.23
Exercised (in dollars per share)	$ 25.34
Forfeited (in dollars per share)	$ 40.65
Outstanding at the end of the period (in dollars per share)	$ 29.45		$ 31.58		$ 32.45
Outstanding and expected to vest at end of the period (in dollars per share)	$ 29.44
Exercisable at end of the period (in dollars per share)	$ 29.40
Weighted-Average Remaining Contractual Life
Outstanding and expected to vest at end of the period	4 years 2 months 12 days
Exercisable at end of the period	3 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	717,000				13,339,000
Outstanding and expected to vest at end of the period (in dollars)	713,000				12,993,000
Exercisable at end of the period (in dollars)	631,000
Closing price of share (in dollars per share)	$ 29.42
Total intrinsic value of options exercised (in dollars)	200,000	700,000
Granted (in shares)	0		0
Number of Shares, Unvested Stock Options
Unvested at the beginning of the period (in shares)	826,000
Vested (in shares)	(212,000)
Forfeited (in shares)	(1,000)
Unvested at the end of the period (in shares)	613,000		826,000
Weighted-Average Grant-Date Fair Value, Unvested Stock Options
Unvested at the beginning of the period (in dollars per share)	$ 10.25
Vested (in dollars per share)	$ 10.17
Forfeited (in dollars per share)	$ 10.33
Unvested at the end of the period (in dollars per share)	$ 10.27		$ 10.25
Unrecognized compensation cost and vesting period
Unrecognized compensation costs related to unvested share-based compensation arrangements	$ 12,800,000
Weighted-average period for recognition of unrecognized stock-based compensation expense	2 years