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Stock Awards - Additional Information (Detail)
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3 Months Ended | 12 Months Ended |
|---|---|---|
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Mar. 31, 2013
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Dec. 31, 2012
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Equity Incentive Plan
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Reserved shares of common stock for awards under the Equity Incentive Plan | 7,441,180 | |
| Common stock remaining for future stock awards | 495,132 | |
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Performance-Based Awards
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Share - based compensation ,shares issued | 204,255 | 252,566 |
| Stock awards vesting period in years | 3 years | |
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Time-Based Awards
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Share - based compensation ,shares issued | 240,425 | 275,464 |
| Stock awards vesting period in years | 3 years | |
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Multi-Year Performance-Based Awards
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Share - based compensation ,shares issued | 550,000 | 649,793 |
| Stock awards vesting period in years | 3 years |