Share-Based Compensation (Details Textual) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-Based Compensation (Textual) [Abstract]
Number of shares available for issuance	7,789,532
Number of shares available for issuance remaining	1,317,205
Stock option granted (shares)	0	0	462,229
Estimated weighted average grant date fair value of stock options (in dollars per share)			$ 5.48
Aggregate intrinsic value of stock options exercised	$ 4.6	$ 11.4	$ 9.9
Tax benefit from stock option exercised	1.8	4.5	3.9
Fair value of options vested during period	1.8	1.8	3.1
Shares of non-vested common stock granted	172,475
Number of restricted stock units granted	253,525
Minimum [Member]
Share-Based Compensation (Textual) [Abstract]
Minimum vesting period of outstanding options and non vested shares (years)	3 years
Expiration period of outstanding options (years)	5 years
Maximum [Member]
Share-Based Compensation (Textual) [Abstract]
Minimum vesting period of outstanding options and non vested shares (years)	6 years
Expiration period of outstanding options (years)	10 years
Employee Stock Option [Member]
Share-Based Compensation (Textual) [Abstract]
Total unrecognized compensation cost related to stock options	1.7
Weighted-average period of recognition of unrecognized compensation cost	1 year 106 days
Compensation cost charged against income	1.6	1.8	1.5
Income tax benefit recognized during the period	0.6	0.7	0.6
Nonvested Stock Awards [Member]
Share-Based Compensation (Textual) [Abstract]
Weighted-average period of recognition of unrecognized compensation cost	2 years 307 days
Compensation cost charged against income	7.5	8.8	11.4
Income tax benefit recognized during the period	2.9	3.4	4.4
Shares of non-vested common stock granted	172,000	211,000
Total unrecognized compensation cost related to stock options	15.5
Restricted Stock Units (RSUs) [Member]
Share-Based Compensation (Textual) [Abstract]
Weighted-average period of recognition of unrecognized compensation cost	3 years 88 days
Compensation cost charged against income	8.1	3.5	1.2
Income tax benefit recognized during the period	3.2	1.4	0.5
Unrecognized compensation cost	$ 14.2
Number of restricted stock units granted	253,000	292,000
Annual award vesting rights, percentage	25.00%
Board Of Directors [Member]
Share-Based Compensation (Textual) [Abstract]
Minimum vesting period of outstanding options and non vested shares (years)	3 years
Shares of non-vested common stock granted	9,676
Board Of Directors [Member] | Nonvested Stock Awards [Member]
Share-Based Compensation (Textual) [Abstract]
Minimum vesting period of outstanding options and non vested shares (years)	3 years
Employees Non Vested Shares One [Member]
Share-Based Compensation (Textual) [Abstract]
Shares of non-vested common stock granted	162,799
Employees - Non Vested Shares Two Member
Share-Based Compensation (Textual) [Abstract]
Minimum vesting period of outstanding options and non vested shares (years)	4 years
Executive Officer [Member]
Share-Based Compensation (Textual) [Abstract]
Minimum vesting period of outstanding options and non vested shares (years)	4 years