Common Stock Plans (Performance Share Awards) (Details) - Performance share awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Weighted Average Price
Share-based compensation expense	$ 6.7	$ 6.2	$ 3.8
Tax benefit related to stock-based compensation	2.4	$ 2.3	$ 1.4
Unrecognized compensation cost	$ 8.9
Weighted average requisite service period	1 year 7 months 28 days
Stock Incentive Plan
Shares
Nonvested, Beginning of Period, Shares	212,968	160,819	0
Forfeited, Shares			(8,008)
Vested and paid, Shares	(77,257)	(14,097)
Nonvested, End of Period, Shares	256,083	212,968	160,819
Weighted Average Price
Nonvested, Beginning of Period, Weighted Average Price (in dollars per share)	$ 71.53	$ 62.13	$ 0.00
Forfeited, Weighted Average Price (in dollars per share)			60.03
Vested and paid, Weighted Average Price (in dollars per share)	61.36	70.06
Nonvested, End of Period, Weighted Average Price (in dollars per share)	$ 80.43	$ 71.53	$ 62.13
Stock Incentive Plan | Two year vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	2 years
Shares
Granted, Shares		937	86,221
Weighted Average Price
Granted, Weighted Average Price (in dollars per share)		$ 131.56	$ 61.14
Stock Incentive Plan | Three year vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	3 years
Shares
Granted, Shares	120,372	65,309	82,606
Weighted Average Price
Granted, Weighted Average Price (in dollars per share)	$ 83.94	$ 93.49	$ 62.96