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Share Based Compensation (Details) (USD $)
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3 Months Ended | 6 Months Ended | 12 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 24 Months Ended | 0 Months Ended | ||||||||
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Jun. 30, 2013
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Mar. 31, 2013
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Jun. 30, 2012
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Mar. 31, 2012
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Jun. 30, 2013
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Jun. 30, 2012
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Dec. 31, 2012
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Dec. 31, 2011
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Jun. 30, 2013
Minimum [Member]
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Jun. 30, 2013
Minimum [Member]
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Jun. 30, 2013
Maximum [Member]
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Jun. 30, 2013
Maximum [Member]
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Jun. 30, 2013
Share Options [Member]
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Jun. 30, 2013
Performance-Based Restricted Share Units [Member]
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Jun. 30, 2013
Performance-Based Restricted Share Units [Member]
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Dec. 31, 2012
Performance-Based Restricted Share Units [Member]
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Feb. 19, 2013
CEO Non-Performance-Based Restricted Share Units [Member]
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Mar. 01, 2012
CEO Non-Performance-Based Restricted Share Units [Member]
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Feb. 19, 2013
Non-CEO Non-Performance-Based Restricted Share Units [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||||||||||||||||||
| Number of shares reserved for issuance under the Plan (in shares) | 10,000,000 | 10,000,000 | |||||||||||||||||
| Portion of options that will become exercisable on the first anniversary of the grant date | 25.00% | ||||||||||||||||||
| Additional options vesting each quarter based on the grantee’s continued employment over a four-year period after the first anniversary | 6.25% | ||||||||||||||||||
| Additional vesting period after first anniversary | 4 years | ||||||||||||||||||
| Award expiration period | 10 years | ||||||||||||||||||
| Share-based compensation expense from adoption of ASC Topic 718 | $ 851,000 | $ 367,000 | $ 1,160,000 | $ 652,000 | $ 0 | $ 0 | |||||||||||||
| Assumptions: | |||||||||||||||||||
| Volatility, minimum | 45.30% | 45.30% | |||||||||||||||||
| Volatility, maximum | 47.60% | 47.60% | |||||||||||||||||
| Risk-free interest rate, minimum | 0.85% | 0.85% | |||||||||||||||||
| Risk-free interest rate, maximum | 1.29% | 1.29% | |||||||||||||||||
| Weighted average expected lives | 6 years 1 month 6 days | 6 years 1 month 6 days | |||||||||||||||||
| Forfeiture rate, minimum | 1.60% | 1.60% | |||||||||||||||||
| Forfeiture rate, maximum | 1.60% | 1.60% | |||||||||||||||||
| Dividend yield rate | 3.04% | 3.04% | 3.55% | 3.55% | |||||||||||||||
| Number of Share Options, Outstanding [Roll Forward] | |||||||||||||||||||
| Outstanding, beginning of period (in shares) | 2,705,027 | 2,795,437 | 2,849,601 | 2,916,143 | 2,795,437 | 2,916,143 | 2,916,143 | ||||||||||||
| Granted (in shares) | 42,500 | 27,000 | 49,000 | 49,500 | |||||||||||||||
| Exercised (in shares) | (73,580) | (4,770) | (170,490) | (40,154) | |||||||||||||||
| Expired (in shares) | (51,033) | ||||||||||||||||||
| Forfeited (in shares) | (372) | (1,250) | (372) | (3,875) | |||||||||||||||
| Outstanding, end of period (in shares) | 2,673,575 | 2,705,027 | 2,870,581 | 2,849,601 | 2,673,575 | 2,870,581 | 2,795,437 | 2,916,143 | |||||||||||
| Weighted Average Exercise Price [Roll Forward] | |||||||||||||||||||
| Outstanding, beginning of period (in dollars per share) | $ 6.82 | $ 6.70 | $ 6.55 | $ 6.61 | $ 6.70 | $ 6.61 | $ 6.61 | ||||||||||||
| Granted (in dollars per share) | $ 10.70 | $ 8.24 | $ 10.61 | $ 8.77 | |||||||||||||||
| Exercised (in dollars per share) | $ 8.06 | $ 3.77 | $ 5.47 | $ 4.06 | |||||||||||||||
| Expired (in dollars per share) | $ 9.86 | ||||||||||||||||||
| Forfeited (in dollars per share) | $ 7.67 | $ 7.21 | $ 7.67 | $ 7.14 | |||||||||||||||
| Outstanding, end of period (in dollars per share) | $ 6.85 | $ 6.82 | $ 6.62 | $ 6.55 | $ 6.85 | $ 6.62 | $ 6.70 | $ 6.61 | |||||||||||
| Weighted Average Remaining Contractual Term [Roll Forward] | |||||||||||||||||||
| Outstanding, beginning of period | 6 years 4 months 21 days | 6 years 6 months 15 days | 7 years 1 month 17 days | 7 years 4 months 6 days | 6 years 10 months 24 days | 7 years 8 months 19 days | 7 years 6 months 18 days | 8 years 4 months 24 days | |||||||||||
| Granted | 9 years 10 months 28 days | 9 years 10 months 17 days | 9 years 6 months 11 days | 9 years 7 months 10 days | |||||||||||||||
| Outstanding, end of period | 6 years 4 months 21 days | 6 years 6 months 15 days | 7 years 1 month 17 days | 7 years 4 months 6 days | 6 years 10 months 24 days | 7 years 8 months 19 days | 7 years 6 months 18 days | 8 years 4 months 24 days | |||||||||||
| Weighted average grant date fair value (in dollars per share) | $ 2.08 | $ 2.00 | $ 2.08 | $ 2.00 | |||||||||||||||
| Unrecognized compensation cost related to non-vested share-based compensation arrangements | $ 1,177,000 | $ 1,927,000 | $ 1,177,000 | $ 1,927,000 | |||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Performance Period | 3 years | 2 years | |||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period | 0 | ||||||||||||||||||
| Units awarded | 149,701 | 86,705 | 95,590 | ||||||||||||||||
| Fair value of awards | $ 10.02 | $ 8.56 | $ 10.02 | ||||||||||||||||
| Life of awards | 36 months | 22 months | |||||||||||||||||
| Annual vesting percentage | 33.33% | 50.00% | |||||||||||||||||