Stock-Based Compensation (Details) (USD $)	6 Months Ended
	Jun. 30, 2014 item
Stock-Based Compensation
Number of equity compensation plans	2
Weighted-Average Grant Date Fair Value
Number of performance measures	2
ROIC
Weighted-Average Grant Date Fair Value
Granted (in dollars per share)	$ 24.72
Performance period	3 years
TSR
Weighted-Average Grant Date Fair Value
Granted (in dollars per share)	$ 30.66
Prior to January 1, 2014 | TSR
Weighted-Average Grant Date Fair Value
Performance period	20 days
Prior to December 31, 2016 | TSR
Weighted-Average Grant Date Fair Value
Performance period	20 days
Stock Option
Options
Outstanding at the beginning of the period (in shares)	1,147,320
Exercised (in shares)	(34,459)
Forfeited (in shares)	(154)
Outstanding at the end of the period (in shares)	1,112,707
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 13.21
Exercised (in dollars per share)	$ 3.91
Forfeited (in dollars per share)	$ 24.45
Outstanding at the end of the period (in dollars per share)	$ 13.49
Restricted stock
Shares
Outstanding at the beginning of the period (in shares)	211,716
Granted (in shares)	82,351
Vested (in shares)	(62,082)
Forfeited (in shares)	(202)
Outstanding unvested at the end of the period (in shares)	231,783
Weighted-Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 21.33
Granted (in dollars per share)	$ 24.46
Vested (in dollars per share)	$ 20.91
Forfeited (in dollars per share)	$ 24.68
Outstanding unvested at the end of the period (in dollars per share)	$ 22.55
Shares received as payment for withholding taxes due by holders of awards	17,961
Performance Awards
Shares
Outstanding at the beginning of the period (in shares)	87,194
Granted (in shares)	85,078
Outstanding unvested at the end of the period (in shares)	172,272
Weighted-Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 21.29
Granted (in dollars per share)	$ 27.69
Outstanding unvested at the end of the period (in dollars per share)	$ 24.45
Performance Awards | ROE
Shares
Outstanding unvested at the end of the period (in shares)	87,194
Performance Awards | ROIC
Shares
Outstanding unvested at the end of the period (in shares)	42,539
Performance Awards | TSR
Shares
Outstanding unvested at the end of the period (in shares)	42,539