Compensation Plans Restricted Stock Units Under the Equity Incentive Compensation Plan (Details) (Restricted Stock Units (RSUs) [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock Units (RSUs) [Member]
Compensation plans
Stock-based compensation expense	$ 13,900,000	$ 13,100,000	$ 9,800,000
Unrecognized stock based compensation expense	22,500,000
Fair value of PSUs/RSUs Granted in Period	19,700,000	19,800,000	18,800,000
Fair value of PSUs/RSUs Vested in Period	$ 14,700,000	$ 10,300,000	$ 5,400,000
Shares Issued in Period	253,031	207,378	166,670
Stock issued for settlement, RSU, net of tax (in shares)	171,597	139,391	116,813
Shares held for settlement of income and payroll tax obligations (in shares)	81,434	67,987	49,857
Number of Shares Represented by Each RSU	1
RSU Vesting Increment	0.33	0.33	0.33
RSUs
Non-vested at the beginning of the period (in shares)	580,431	496,244	308,877
Granted (in shares)	234,560	329,939	379,332
Vested (in shares)	(253,031)	(207,376)	(166,672)
Forfeited (in shares)	(46,236)	(38,376)	(25,293)
Non-vested at the end of the period (in shares)	515,724	580,431	496,244
Weighted- Average Grant-Date Fair Value
Non-vested outstanding at the beginning of the period (in dollars per share)	$ 57.05	$ 51.81	$ 44.33
Granted (in dollars per share)	$ 83.98	$ 60.01	$ 49.47
Vested (in dollars per share)	$ 58.19	$ 49.73	$ 32.72
Forfeited (in dollars per share)	$ 62.06	$ 54.37	$ 51.06
Non-vested outstanding at the end of the period (in dollars per share)	$ 68.29	$ 57.05	$ 51.81