Stock-Based Compensation (Details) (USD $)	6 Months Ended				6 Months Ended					6 Months Ended		6 Months Ended
	Jun. 30, 2013 Stock Options item	Jun. 30, 2013 Restricted Stock, Restricted Stock Units, Cash Settled Restricted Stock Units and Cash Settled Performance Awards item	Jun. 30, 2013 Cash settled restricted stock units and cash settled performance awards	Jun. 30, 2013 Restricted stock shares and stock settled restricted stock units	Jun. 30, 2013 Partnership Phantom Units	Apr. 30, 2013 2013 Plan	Jun. 30, 2013 2013 Plan Stock Options	Jun. 30, 2013 2013 Plan Stock Appreciation Rights	Jun. 30, 2013 2013 Plan Stock-settled award other than an option, stock appreciation right or award for which the recipient pays intrinsic value	Jun. 30, 2013 Employee Stock Purchase Plan	May 31, 2011 Employee Stock Purchase Plan	Jun. 30, 2013 Employee Stock Purchase Plan Minimum	Jun. 30, 2013 Employee Stock Purchase Plan Maximum	Jun. 30, 2013 Partnership Long-Term Incentive Plan
Stock-based compensation
Maximum number of shares available under the Plan						6,500,000					1,000,000			1,035,378
Number of shares counted by each award							1	1	1.75
Expiration period	7 years
Vesting of awards per anniversary or year (as a percent)	33.33%	33.33%
Number of anniversaries of grant date on which awards will vest	3	3
Weighted average grant date fair value (in dollars per share)	$ 10.19
Weighted average assumptions
Expected life	4 years 6 months
Risk-free interest rate (as a percent)	0.66%
Volatility (as a percent)	49.19%
Dividend yield (as a percent)	0.00%
Stock Options
Options outstanding at the beginning of the period (in shares)	2,584,000
Granted (in shares)	177,000
Exercised (in shares)	(309,000)
Cancelled (in shares)	(11,000)
Options outstanding at the end of the period (in shares)	2,441,000
Options exercisable at the end of the period (in shares)	1,731,000
Weighted Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)	$ 27.02
Granted (in dollars per share)	$ 25.04
Exercised (in dollars per share)	$ 17.64
Cancelled (in dollars per share)	$ 48.96
Options outstanding at end of period, (in dollars per share)	$ 27.96
Options exercisable at the end of period (in dollars per share)	$ 33.00
Weighted Average Remaining Life
Outstanding at the end of the period	3 years 9 months 18 days
Exercisable at the end of the period	3 years
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 19,060,000
Exercisable at the end of the period (in dollars)	10,215,000
Total intrinsic value of stock options exercised (in dollars)	2,800,000
Unrecognized compensation
Expected unrecognized compensation cost related to unvested stock options (in dollars)	3,300,000	32,300,000			1,900,000
Weighted-average period over which the expected unrecognized compensation cost related to unvested stock options will be recognized	1 year 8 months 12 days	1 year 10 months 24 days			2 years 1 month 6 days
Shares
Non-vested awards at the beginning of the period (in shares)		1,992,000	472,000	1,443,000	64,000
Granted (in shares)		701,000			55,000
Vested (in shares)		(756,000)			(20,000)
Cancelled (in shares)		(22,000)
Non-vested awards at the end of the period (in shares)		1,915,000	472,000	1,443,000	99,000
Weighted Average Grant-Date Fair Value Per Share
Non-vested awards at the beginning of the period (in dollars per share)		$ 16.12			$ 23.62
Granted (in dollars per share)		$ 25.10			$ 23.76
Vested (in dollars per share)		$ 18.63			$ 24.28
Cancelled (in dollars per share)		$ 19.43
Non-vested awards at the end of the period (in dollars per share)		$ 18.38			$ 23.57
Employee Stock Purchase Plan
Maximum employee salary to purchase shares (in dollars)										$ 25,000
Maximum percentage of employee eligible pay to purchase shares										10.00%
Purchase price as a percent of the fair market value												85.00%	100.00%
Remaining shares available for purchase										269,540
Employee Stock Purchase plan discount from market price (as a percent)										5.00%