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Our Portfolio - Financing Receivables, Investments and Real Estate - Additional Information (Detail) (USD $)
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3 Months Ended | 6 Months Ended | 9 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 9 Months Ended | |||||||||
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Sep. 30, 2014
Investment
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Jun. 30, 2014
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Sep. 30, 2013
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Sep. 30, 2014
Investment
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Sep. 30, 2014
Investment
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Sep. 30, 2013
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Mar. 31, 2014
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Dec. 31, 2013
Investment
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Sep. 30, 2014
November 2014 [Member]
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Sep. 30, 2013
Energy Source [Member]
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Sep. 30, 2013
Energy Source [Member]
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Sep. 30, 2014
Energy Source [Member]
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Dec. 31, 2013
Energy Source [Member]
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May 31, 2013
Energy Source [Member]
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Sep. 30, 2014
Minimum [Member]
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Sep. 30, 2014
Maximum [Member]
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| Financing Receivable, Recorded Investment [Line Items] | ||||||||||||||||
| Financing receivables and investments | $ 610,100,000 | $ 610,100,000 | $ 610,100,000 | |||||||||||||
| Deferred funding obligations | 49,700,000 | 49,700,000 | 49,700,000 | 74,700,000 | ||||||||||||
| Restricted cash | 4,900,000 | 4,900,000 | 4,900,000 | 49,900,000 | ||||||||||||
| Available-for-sale debt securities at fair value | 43,600,000 | 43,600,000 | 43,600,000 | 3,200,000 | ||||||||||||
| Investments designated as held-to-maturity carrying value | 14,700,000 | |||||||||||||||
| Sale of investments designated as held-to-maturity | 15,500,000 | |||||||||||||||
| Realized gain on sale of investments designated as held-to-maturity | 800,000 | |||||||||||||||
| Available-for-sale debt securities sold at fair value | 43,600,000 | |||||||||||||||
| Available-for-sale debt securities at cost | 41,400,000 | 41,400,000 | 41,400,000 | |||||||||||||
| Realized gain on sale of investments | 2,200,000 | 2,200,000 | ||||||||||||||
| Investments in unrealized loss position | 0 | 0 | 0 | 0 | ||||||||||||
| Lease agreement expected expirations, term | 2052 | 2061 | ||||||||||||||
| Financing receivable allowance | 11,000,000 | 11,000,000 | 11,000,000 | 11,000,000 | ||||||||||||
| Financing receivable allowance, face amount | 24,000,000 | |||||||||||||||
| Accrued interest income | 0 | 400,000 | 0 | 600,000 | ||||||||||||
| Financial receivable average outstanding balance | 11,800,000 | |||||||||||||||
| Income on investment | 4,269,000 | 2,590,000 | 9,744,000 | 4,397,000 | 100,000 | 500,000 | ||||||||||
| Maximum exposure loss for variable interest entity | 800,000 | |||||||||||||||
| Loan expected recovery | 800,000 | |||||||||||||||
| Maximum agreed recovery amount | 2,000,000 | |||||||||||||||
| Other financing receivables on non accrual status | 0 | 0 | 0 | 0 | ||||||||||||
| Provision for credit losses | $ 0 | $ 0 | $ 0 | $ 0 | ||||||||||||