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Stock Option Plans and Share-Based Compensation Performance based stock units (PSU) (Details) (USD $)
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3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 0 Months Ended | 9 Months Ended | 0 Months Ended | 12 Months Ended | 9 Months Ended | 3 Months Ended | ||||||||||||
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Sep. 30, 2013
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Sep. 30, 2012
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Sep. 30, 2013
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Sep. 30, 2012
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Sep. 30, 2013
Performance Shares [Member]
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Sep. 30, 2012
Performance Shares [Member]
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Sep. 30, 2013
Performance Shares [Member]
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Sep. 30, 2012
Performance Shares [Member]
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Dec. 31, 2011
Performance Shares [Member]
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Jun. 30, 2013
Performance Shares [Member]
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Dec. 31, 2012
Performance Shares [Member]
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Sep. 30, 2013
PSU program year one [Member]
Performance Shares [Member]
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Jan. 17, 2012
2011 PSU [Member]
Performance Shares [Member]
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Mar. 05, 2013
2013 PSU [Member]
Performance Shares [Member]
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Sep. 30, 2013
2013 PSU [Member]
Performance Shares [Member]
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Jan. 22, 2013
2012 PSU [Member]
Performance Shares [Member]
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Dec. 31, 2012
2012 PSU [Member]
Performance Shares [Member]
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Sep. 30, 2013
Below the 35th percentile ranking [Member]
PSU Program Year Two [Member]
Performance Shares [Member]
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Sep. 30, 2013
Below the 35th percentile ranking [Member]
2011 PSU [Member]
Performance Shares [Member]
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Sep. 30, 2013
At least 50th percentile (after yr one) [Member]
PSU Program Year Two [Member]
Performance Shares [Member]
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Sep. 30, 2013
Below 50th percentile ranking [Member]
PSU Program Year Two [Member]
Performance Shares [Member]
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Sep. 30, 2013
Below 50th percentile ranking [Member]
2011 PSU [Member]
Performance Shares [Member]
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Sep. 30, 2013
Minimum [Member]
Below the 75th percentile ranking [Member]
PSU program year one [Member]
Performance Shares [Member]
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Sep. 30, 2013
Maximum [Member]
Below the 75th percentile ranking [Member]
PSU program year one [Member]
Performance Shares [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||||||||||||||||||
| PSU percentage eligible for time-based vesting | 0.00% | 0.00% | 100.00% | 50.00% | 50.00% | 110.00% | 119.00% | |||||||||||||||||
| Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Share-based Awards Other than Options | $ 1,500,000 | $ 1,500,000 | ||||||||||||||||||||||
| Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition | 1 year 4 months 6 days | |||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | 253,000 | 175,000 | ||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ 13.07 | $ 13.07 | $ 11.00 | |||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 140,000 | 100,000 | 12,500 | 125,000 | 125,000 | |||||||||||||||||||
| PSU shares eligible for vesting based on actual shareholder return | 120,000 | 120,000 | 62,500 | |||||||||||||||||||||
| Share-based Compensation Arrangement By Share-based Payment Award, Number Of Shares Eligible For Vesting | 62,500 | |||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period | 38,000 | |||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 14.74 | |||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value | $ 11.02 | |||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period | 24,000 | |||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value | $ 0.00 | |||||||||||||||||||||||
| Allocated Share-based Compensation Expense | $ 2,810,000 | $ 2,361,000 | $ 8,423,000 | $ 6,781,000 | $ 400,000 | $ 200,000 | $ 1,200,000 | $ 800,000 | ||||||||||||||||
| Percentile ranking of 2011 shareholder return | 76.30% | 35.30% | ||||||||||||||||||||||
| PSU percentage eligible for vesting based on actual return | 120.00% | 50.00% | ||||||||||||||||||||||
| Share-based Compensation Arrangement by Share-based payment Award, Percent Vested in First Year | 0.00% | |||||||||||||||||||||||