Stock-Based Compensation Plans - Summary of Activity for Performance Share and Performance Units (Details) (Amended and Restated 2004 Stock Incentive Plan, USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Performance Shares Awards
Shares/Units
Unvested as of beginning of the period	1,139
Granted	22
Vested	(462)
Forfeited	(111)
Unvested as of end of period	588	1,139
Weighted Average Grant Date Fair Value per Share (in dollars per share)
Unvested as of beginning of the period	$ 51.87
Granted	$ 70.96	$ 56.32	$ 45.91
Vested	$ 50.82
Forfeited	$ 52.28
Unvested as of end of the period	$ 53.33	$ 51.87
Performance Share Units
Shares/Units
Unvested as of beginning of the period	864
Granted	1,096
Vested	(289)
Forfeited	(147)
Unvested as of end of period	1,524	864
Weighted Average Grant Date Fair Value per Share (in dollars per share)
Unvested as of beginning of the period	$ 50.21
Granted	$ 68.66	$ 52.05	$ 39.07
Vested	$ 48.33
Forfeited	$ 66.70
Unvested as of end of the period	$ 62.25	$ 50.21