Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation
Compensation expense related to the Plan	$ 23.1	$ 20.4	$ 17.8
Restricted Stock
Stock-based compensation
Number of shares ranted (in shares)	439,633	280,830	524,063
Period over which forfeiture and non-transferable restrictions lapse	4 years
Percentage over which unrecognized compensation cost is expected to be recognized year one	15.00%
Percentage over which unrecognized compensation cost is expected to be recognized year two	15.00%
Percentage over which unrecognized compensation cost is expected to be recognized year three	20.00%
Percentage over which unrecognized compensation cost is expected to be recognized year four	50.00%
Unrecognized compensation cost related to the restricted stock	$ 34.2
Shares
Balance at the beginning of the period (in shares)	1,027,735	1,126,705
Granted (in shares)	439,633	280,830	524,063
Vested (in shares)	(355,697)	(357,295)
Forfeited (in shares)	(28,827)	(22,505)
Balance at the end of the period (in shares)	1,082,844	1,027,735	1,126,705
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)	$ 47.75	$ 46.55
Granted (in dollars per share)	65.81	51.61
Vested (in dollars per share)	50.85	44.85
Forfeited (in dollars per share)	47.61	46.08
Balance at the end of the period (in dollars per share)	$ 56.26	$ 47.75	$ 46.55
Aggregate Intrinsic Value
Balance at the end of the period	$ 116.1	$ 61.0
2015 Plan
Stock-based compensation
Maximum number of shares authorized under the plan (in shares)	5,000,000
Number of shares of common stock available for grant under the plan (in shares)	4,496,793