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Nonrecourse Debt - Analysis of Nonrecourse Debt by Interest Rate (Parenthetical) (Detail)
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Jun. 30, 2013
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Dec. 31, 2012
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Fixed-rate promissory notes, interest rates from 2.06% to 5.00% per annum [Member] | Minimum [Member]
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| Long Term Debt Maturity [Line Items] | ||
| Fixed-rate promissory notes, interest rates | 2.06% | |
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Fixed-rate promissory notes, interest rates from 2.06% to 5.00% per annum [Member] | Maximum [Member]
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| Long Term Debt Maturity [Line Items] | ||
| Fixed-rate promissory notes, interest rates | 5.00% | |
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Fixed-rate promissory notes, interest rates from 2.26% to 5.00% per annum [Member] | Minimum [Member]
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| Long Term Debt Maturity [Line Items] | ||
| Fixed-rate promissory notes, interest rates | 2.26% | |
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Fixed-rate promissory notes, interest rates from 2.26% to 5.00% per annum [Member] | Maximum [Member]
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| Long Term Debt Maturity [Line Items] | ||
| Fixed-rate promissory notes, interest rates | 5.00% | |
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Fixed-rate promissory notes, interest rates from 5.01% to 6.50% per annum [Member] | Minimum [Member]
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| Long Term Debt Maturity [Line Items] | ||
| Fixed-rate promissory notes, interest rates | 5.01% | 5.01% |
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Fixed-rate promissory notes, interest rates from 5.01% to 6.50% per annum [Member] | Maximum [Member]
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| Long Term Debt Maturity [Line Items] | ||
| Fixed-rate promissory notes, interest rates | 6.50% | 6.50% |
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Fixed-rate promissory notes, interest rates from 6.51% to 8.00% per annum [Member] | Minimum [Member]
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| Long Term Debt Maturity [Line Items] | ||
| Fixed-rate promissory notes, interest rates | 6.51% | 6.51% |
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Fixed-rate promissory notes, interest rates from 6.51% to 8.00% per annum [Member] | Maximum [Member]
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| Long Term Debt Maturity [Line Items] | ||
| Fixed-rate promissory notes, interest rates | 8.00% | 8.00% |