Summary of Significant Accounting Policies (Narrative) (Detail) $ in Millions	9 Months Ended
Sep. 30, 2016 USD ($)	Jul. 01, 2016	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Number of Operating Segments	2
Number of notes receivable investments on non-accrual	4			3
Business Acquisition, Percentage of Voting Interests Acquired		6.00%
Noncontrolling interest subject to vesting and repurchase (percentage)	80.00%
Unamortized Debt Issuance Expense	$ 2.6			$ 4.0
Deferred Tax Assets, Gross, Current			$ 1.0
New accounting pronouncement not yet applied - Retained Earnings Effect	7.5
Non-accrual notes receivable [Member]
Accounts and Notes Receivable, Net	155.4			103.2
Notes Receivable, Fair Value Disclosure	$ 160.3			$ 109.2

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Noncontrolling interest subject to vesting and repurchase (percentage)

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Carrying amount as of the balance sheet date, net of allowance for doubtful accounts, of account and note receivables due from other than related parties.

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards classified as current.

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Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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