Equity-Based Compensation (Details 4) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Additional disclosures
Equity-based compensation expense, net of forfeitures, attributable to future periods (in dollars)	$ 16.0
Restricted stock units
Unvested Restricted Stock Units
Outstanding at beginning of year (in shares)	373,676
Granted (in shares)	270,525
Vested (in shares)	(152,889)
Forfeited (in shares)	(25,918)
Outstanding at end of year (in shares)	465,394	373,676
Outstanding at end of year and expected to vest (in shares)	382,897
Weighted Average Grant Date Fair Value
Outstanding at beginning of year (in dollars per share)	$ 17.02
Granted (in dollars per share)	$ 16.31	$ 15.64	$ 15.99
Vested (in dollars per share)	$ 18.44
Forfeited (in dollars per share)	$ 20.77
Outstanding at end of year (in dollars per share)	$ 17.28	$ 17.02
Outstanding at end of year and expected to vest (in dollars per share)	$ 17.26
Additional disclosures
Total grant date fair value	2.8	3.5	3.1
Equity-based compensation expense, net of forfeitures, attributable to future periods (in dollars)	4.5
Weighted average amortization periods	2 years 1 month 6 days
Stock options
Additional disclosures
Equity-based compensation expense, net of forfeitures, attributable to future periods (in dollars)	$ 11.5
Weighted average amortization periods	2 years 8 months 12 days
2007 Equity Incentive Plan
Unvested Restricted Stock Units
Outstanding at end of year (in shares)	290,394
2007 Equity Incentive Plan | Restricted stock units
Equity compensation plans
Shares issued	270,525
Award vesting period	4 years