Stock-Based Compensation Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Stock Options Activity [Roll Forward]
Options exercised - employees (in shares)	(88,661)	0
Weighted Average Exercise Price [Roll Forward]
Options exercised - employees (in dollars per share)	$ 12.50	$ 0
Weighted Average Remaining Contractual Term [Abstract]
Stock-based compensation expense recorded	$ 0.3	$ 0.3
Aggregate Intrinsic Value [Abstract]
Closing stock price (in dollars per share)	$ 28.82
Stock Options [Member]
Stock Options Activity [Roll Forward]
Options outstanding at beginning of period (in shares)	1,335,680	1,192,680
Options granted - directors and employees (in shares)	0	0
Options forfeited - employees (in shares)	(834)	0
Options outstanding at end of period (in shares)	1,246,185	1,192,680
Options exercisable at December 31, 2012 (in shares)	981,310	832,055
Weighted Average Exercise Price [Roll Forward]
Outstanding at beginning of period (in dollars per share)	$ 13.41	$ 12.89
Granted - directors and employees (in dollars per share)	$ 0	$ 0
Forfeited - employees (in dollars per share)	$ 5.60	$ 0
Outstanding at end of period (in dollars per share)	$ 13.48	$ 12.89
Exercisable at December 31, 2012 (in dollars per share)	$ 11.99	$ 11.12
Weighted Average Remaining Contractual Term [Abstract]
Weighted average remaining term of the stock options exercisable (in years)	5 years 8 months 12 days	6 years 2 months 12 days
Vesting period of stock options (in years)	4 years
Percentage of stock options vesting after one year (in hundredths)	25.00%
Percentage of stock options vesting each month following first year (in hundredths)	2.083%
Aggregate Intrinsic Value [Abstract]
Aggregate intrinsic value of options exercised	1.3
Aggregate intrinsic value of options outstanding	19.1
Stock Options [Member] | Directors [Member]
Weighted Average Remaining Contractual Term [Abstract]
Remaining unamortized stock-based compensation cost	0.1
Stock-based compensation cost recognition period	2 months
Stock Options [Member] | Employees [Member]
Weighted Average Remaining Contractual Term [Abstract]
Remaining unamortized stock-based compensation cost	1.9
Stock-based compensation cost recognition period	2 years 4 months 24 days
Restricted Stock [Member]
Weighted Average Remaining Contractual Term [Abstract]
Vesting period of stock options (in years)	1 year
Restricted Stock Grant [Abstract]
Restricted stock granted (in shares)	2,500
Restricted Stock [Member] | Maximum [Member]
Restricted Stock Grant [Abstract]
Restricted common stock value	$ 0.1