Common Stock Plans (Restricted Stock) (Details) - Restricted Stock and Restricted Stock Units - Stock Incentive Plan - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 6.0	$ 3.2	$ 1.9
Tax benefit related to stock-based compensation	2.1	$ 1.2	$ 0.7
Unrecognized compensation cost	$ 1.9
Remaining requisite service period (in years)	1 year 9 months
Shares
Nonvested, Beginning of Period, Shares	99,574	62,518	11,115
Granted, Shares	99,814	48,904	52,650
Forfeited, Shares			(1,247)
Vested, Shares	(14,446)	(11,848)
Nonvested, End of Period, Shares	184,942	99,574	62,518
Weighted Average Price
Nonvested, Beginning of Period, Weighted Average Price (in dollars per share)	$ 59.60	$ 51.16	$ 45.24
Granted, Weighted Average Price (in dollars per share)	65.15	71.91	52.34
Forfeited, Weighted Average Price (in dollars per share)			48.36
Vested and paid, Weighted Average Price (in dollars per share)	53.20	65.94
Nonvested, End of Period, Weighted Average Price (in dollars per share)	$ 63.09	$ 59.60	$ 51.16