Stock Based Compensation - Restricted Stock Rollforward (Details) (USD $)	6 Months Ended
Jun. 30, 2012
Restricted Stock LTIP Plan
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning Balance	169,863
Nonvested Stock Awards Granted	42,754
Nonvested Stock Awards Vested	(79,519)
Nonvested Stock Awards Forfeited	(5,104)
Ending Balance	127,994
Weighted Average Grant Date Fair Value, Nonvested Stock Awards, Beginning of Period	$ 20.66
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Granted	$ 39.43
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Vested	$ 12.33
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Forfeited	$ 28.32
Weighted Average Grant Date Fair Value, Nonvested Stock Awards, End of Period	$ 31.79
Restricted Stock Units (RSUs) LTIP Plan
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning Balance	0
Nonvested Stock Awards Granted	2,100
Nonvested Stock Awards Vested	0
Nonvested Stock Awards Forfeited	0
Ending Balance	2,100
Weighted Average Grant Date Fair Value, Nonvested Stock Awards, Beginning of Period	$ 0.00
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Granted	$ 38.13
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Vested	$ 0.00
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Forfeited	$ 0.00
Weighted Average Grant Date Fair Value, Nonvested Stock Awards, End of Period	$ 38.13
Restricted Stock GAIP Plan
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning Balance	62,250
Nonvested Stock Awards Granted	0
Nonvested Stock Awards Vested	59,850
Nonvested Stock Awards Forfeited	2,400
Ending Balance	0
Weighted Average Grant Date Fair Value, Nonvested Stock Awards, Beginning of Period	$ 7.72
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Granted	$ 0.00
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Vested	$ 7.72
Weighted Average Grant Date Fair Value, Nonvested Stock Awards Forfeited	$ 7.72
Weighted Average Grant Date Fair Value, Nonvested Stock Awards, End of Period	$ 0.00

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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