Performance Share Unit Activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Shares
Granted, Shares	200,000	200,000	300,000
Weighted-Average Grant Date Fair Value
Nonvested, Weighted-Average Grant Date Fair Value, Beginning Balance	$ 40.27
Granted, Weighted-Average Grant Date Fair Value	$ 56.20
Vested, Weighted-Average Grant Date Fair Value	$ 38.50
Forfeited, Weighted-Average Grant Date Fair Value	$ 53.58
Nonvested, Weighted-Average Grant Date Fair Value, Ending Balance	$ 40.27	$ 40.27
Performance Shares [Member]
Shares
Nonvested, Beginning Balance	0
Granted, Shares	54,065
Vested, Shares	0
Forfeited, Shares	(860)
Nonvested, Ending Balance	53,205
Weighted-Average Grant Date Fair Value
Nonvested, Weighted-Average Grant Date Fair Value, Beginning Balance	$ 0.00
Granted, Weighted-Average Grant Date Fair Value	$ 59.58
Vested, Weighted-Average Grant Date Fair Value	$ 0.00
Forfeited, Weighted-Average Grant Date Fair Value	$ 59.58
Nonvested, Weighted-Average Grant Date Fair Value, Ending Balance	$ 59.58