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Stock-Based Compensation Plans (Details 3) (USD $)
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12 Months Ended | 12 Months Ended | ||||||||||||||||
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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Dec. 31, 2012
Stock Options
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Dec. 31, 2011
Stock Options
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Dec. 31, 2010
Stock Options
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Dec. 31, 2012
Restricted stock
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Dec. 31, 2011
Restricted stock
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Dec. 31, 2010
Restricted stock
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Dec. 31, 2012
Restricted stock
Minimum
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Dec. 31, 2012
Restricted stock
Maximum
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Dec. 31, 2012
Non-Qualified Employee Stock Purchase Plan
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Dec. 31, 2011
Non-Qualified Employee Stock Purchase Plan
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Dec. 31, 2010
Non-Qualified Employee Stock Purchase Plan
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Dec. 31, 1996
Non-Qualified Employee Stock Purchase Plan
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Dec. 31, 2012
Non-Qualified Employee Stock Purchase Plan
Full-time employees
Minimum
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Dec. 31, 2012
Non-Qualified Employee Stock Purchase Plan
Other than full time employees
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May 21, 2009
2009 Plan
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| Additional disclosures | ||||||||||||||||||
| Weighted average fair value per share (in dollars per share) | $ 29.11 | $ 29.40 | $ 19.45 | |||||||||||||||
| Weighted average assumptions | ||||||||||||||||||
| Expected life of option | 5 years | 7 years | 7 years | |||||||||||||||
| Dividend yield (as a percent) | 3.50% | 4.00% | 5.50% | |||||||||||||||
| Volatility (as a percent) | 35.00% | 35.00% | 43.00% | |||||||||||||||
| Risk-free interest rate (as a percent) | 0.87% | 3.04% | 3.15% | |||||||||||||||
| Additional disclosures | ||||||||||||||||||
| Outstanding unvested shares granted | 202,218 | 431,320 | ||||||||||||||||
| Restricted stock issued | 96,592 | |||||||||||||||||
| Restricted stock vesting during period | $ 12,883,000 | |||||||||||||||||
| Shares vested | 318,726 | |||||||||||||||||
| Grant date fair value per share (in dollars per share) | $ 48.60 | $ 149.05 | ||||||||||||||||
| Total fair value of shares vested | 36,337,000 | 35,029,000 | 9,805,000 | |||||||||||||||
| Stock-based compensation expense | 9,961,000 | 9,721,000 | 9,906,000 | 127,000 | 216,000 | 272,000 | ||||||||||||
| Capitalized stock-based compensation cost | 5,140,000 | 5,284,000 | 5,117,000 | |||||||||||||||
| Unrecognized compensation cost for unvested stock options | 2,230,000 | |||||||||||||||||
| Unrecognized compensation cost for unvested restricted stock | 6,705,000 | |||||||||||||||||
| Weighted average period for recognition of unrecognized compensation cost | 1 year 8 months 23 days | 2 years 3 months 29 days | ||||||||||||||||
| Forfeiture rate (as a percent) | 1.50% | |||||||||||||||||
| Employee Stock Purchase Plan | ||||||||||||||||||
| Employee stock purchase plan, shares of common stock reserved for issuance | 1,000,000 | |||||||||||||||||
| Employee stock purchase plan, remaining shares of common stock available for issuance | 733,935 | 1,269,822 | ||||||||||||||||
| Employment period for applicability of Employee Stock Purchase Plan | 1 month | 12 months | ||||||||||||||||
| Purchase period | 7 months | |||||||||||||||||
| Employee stock purchase plan, discounted stock price percentage | 85.00% | |||||||||||||||||
| Shares issued under employee stock purchase plan | 6,260 | 6,260 | 6,972 | 8,137 | ||||||||||||||
| Stock-based compensation expense | $ 9,961,000 | $ 9,721,000 | $ 9,906,000 | $ 127,000 | $ 216,000 | $ 272,000 | ||||||||||||