Share-Based Compensation Plans - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized under employee stock purchase plan (in shares)	3,250,000
Shares available for grant or issuance under share-based compensation plans (in shares)	2,086,953
Compensation expense to be recognized	$ 4,500,000
Maximum vesting period	3 years
Proceeds from exercise of stock options	6,900,000	5,200,000	8,800,000
Income tax benefit realized from exercise of stock options	8,600,000	5,200,000	8,700,000
Excess tax benefits from share-based compensation	8,264,000	4,624,000	7,083,000
Total intrinsic value of options exercised	23,500,000	12,500,000	25,900,000
Options that were exercisable (in shares)	566,774	1,310,697	1,796,377
Weighted average exercise price of exercisable options (in dollars per share)	$ 24.15	$ 18.12	$ 17.15
Total intrinsic value of options outstanding and exercisable	11,500,000	31,900,000	31,400,000
Forfeitures of stock options (in shares)			0
Awards of Shares and Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	8,100,000	6,900,000	6,700,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	0	0	11,702
Compensation expense	$ 0	$ 0	$ 100,000
Options outstanding	566,774	1,310,697	1,796,377	3,400,541
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested, but issuance deferred (in shares)	76,001
Issuance deferral period	5 years
Employee Stock Purchase Plan (in shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized under employee stock purchase plan (in shares)	3,000,000
Non-Employee Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	0	0	12,264