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Credit Agreement - Additional Information (Detail) (USD $)
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12 Months Ended | |||
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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Apr. 30, 2008
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| Debt And Credit Agreements [Line Items] | ||||
| Secured revolving credit facility | $ 30,000,000 | |||
| Maturity period description | Through to April 1, 2014 | |||
| Borrowings under the credit agreement | $ 0 | $ 0 | $ 0 | |
| Amended Credit Agreement | ||||
| Debt And Credit Agreements [Line Items] | ||||
| Maturity period | Apr. 01, 2017 |