Stock Based Compensation Plan (Details) (USD $) | 3 Months Ended |
In Millions, except Share data, unless otherwise specified | Mar. 31, 2015 | Mar. 31, 2014 |
Weighted-Average Award Price [Roll Forward] | | |
Period of restrictions over awards | 4 years | |
Compensation expense | $1.10 | $0.90 |
Total compensation cost related to unvested equity awards | 7.5 | |
Weighted-average period of recognition of cost | 2 years 6 months | |
Restricted Stock Award [Member] | | |
Shares or Units and Rights [Roll Forward] | | |
Outstanding, beginning balance (in shares) | 321,322 | |
Granted (in shares) | 171,485 | |
Restrictions lapsed or exercised (in shares) | 0 | |
Forfeited (in shares) | -2,802 | |
Outstanding, ending balance (in shares) | 490,005 | |
Exercisable, ending balance (in shares) | 0 | |
Weighted-Average Award Price [Roll Forward] | | |
Outstanding, beginning balance (in dollars per share) | $20.49 | |
Granted (in dollars per share) | $24 | |
Restrictions lapsed or exercised (in dollars per share) | $0 | |
Forfeited (in dollars per share) | $24.74 | |
Outstanding, ending balance (in dollars per share) | $21.69 | |
Exercisable, ending balance (in dollars per share) | $0 | |
Vesting period | 3 years | |
Aggregate intrinsic value of outstanding awards | 12.2 | |
Stock-Settled Appreciation Rights [Member] | | |
Shares or Units and Rights [Roll Forward] | | |
Outstanding, beginning balance (in shares) | 129,975 | |
Granted (in shares) | 0 | |
Restrictions lapsed or exercised (in shares) | -19,100 | |
Forfeited (in shares) | 0 | |
Outstanding, ending balance (in shares) | 110,875 | |
Exercisable, ending balance (in shares) | 32,875 | |
Weighted-Average Award Price [Roll Forward] | | |
Outstanding, beginning balance (in dollars per share) | $16.04 | |
Granted (in dollars per share) | $0 | |
Restrictions lapsed or exercised (in dollars per share) | $8.74 | |
Forfeited (in dollars per share) | $0 | |
Outstanding, ending balance (in dollars per share) | $17.29 | |
Exercisable, ending balance (in dollars per share) | $15.28 | |
Aggregate intrinsic value of vested awards | 0.3 | |
Aggregate intrinsic value of outstanding awards | $0.80 | |
Performance Shares [Member] | | |
Shares or Units and Rights [Roll Forward] | | |
Granted (in shares) | 52,377 | |