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Share Based Compensation (Details) (USD $)
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3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 24 Months Ended | 0 Months Ended | |||||||
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Sep. 30, 2013
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Sep. 30, 2012
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Jun. 30, 2013
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Jun. 30, 2012
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Sep. 30, 2013
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Sep. 30, 2012
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Dec. 31, 2012
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Dec. 31, 2011
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Sep. 30, 2013
Minimum [Member]
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Sep. 30, 2013
Minimum [Member]
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Sep. 30, 2013
Maximum [Member]
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Sep. 30, 2013
Maximum [Member]
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Sep. 30, 2013
Share Options [Member]
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Sep. 30, 2013
Performance-Based Restricted Share Units [Member]
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Sep. 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 | $ 508,000 | $ 343,000 | $ 1,668,000 | $ 995,000 | $ 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) | 2,673,575 | 2,870,581 | 2,795,437 | 2,916,143 | 2,795,437 | 2,916,143 | 2,916,143 | ||||||||||||
| Granted (in shares) | 49,000 | 49,500 | |||||||||||||||||
| Exercised (in shares) | (98,611) | (20,907) | (269,101) | (61,061) | |||||||||||||||
| Expired (in shares) | (628) | (52,251) | (628) | (103,284) | |||||||||||||||
| Forfeited (in shares) | (112,474) | (7,465) | (112,846) | (11,340) | |||||||||||||||
| Outstanding, end of period (in shares) | 2,461,862 | 2,789,958 | 2,673,575 | 2,870,581 | 2,461,862 | 2,789,958 | 2,795,437 | 2,916,143 | |||||||||||
| Weighted Average Exercise Price [Roll Forward] | |||||||||||||||||||
| Outstanding, beginning of period (in dollars per share) | $ 6.85 | $ 6.62 | $ 6.70 | $ 6.61 | $ 6.70 | $ 6.61 | $ 6.61 | ||||||||||||
| Granted (in dollars per share) | $ 10.61 | $ 8.77 | |||||||||||||||||
| Exercised (in dollars per share) | $ 7.12 | $ 4.36 | $ 6.08 | $ 4.16 | |||||||||||||||
| Expired (in dollars per share) | $ 7.67 | $ 9.90 | $ 7.67 | $ 9.88 | |||||||||||||||
| Forfeited (in dollars per share) | $ 8.52 | $ 7.76 | $ 8.52 | $ 7.54 | |||||||||||||||
| Outstanding, end of period (in dollars per share) | $ 6.76 | $ 6.58 | $ 6.85 | $ 6.62 | $ 6.76 | $ 6.58 | $ 6.70 | $ 6.61 | |||||||||||
| Weighted average contractual term | 6 years 4 months 21 days | 7 years 1 month 17 days | 6 years | 6 years 10 months 24 days | 6 years 9 months | 7 years 6 months 18 days | |||||||||||||
| Weighted average grant date fair value (in dollars per share) | $ 2.04 | $ 2.00 | $ 2.04 | $ 2.00 | |||||||||||||||
| Unrecognized compensation cost related to non-vested share-based compensation arrangements | $ 707,000 | $ 1,630,000 | $ 707,000 | $ 1,630,000 | |||||||||||||||
| 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% | |||||||||||||||||