Acquisitions - Consideration (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Business Combinations [Abstract]
Cash (including debt repaid at closing)	$ 330,929	$ 857,219
Repayment of preferred equity interest and mezzanine loan	51,775	160,123	0
Issuance of OP Units	18,256	0
Gain on Sale and Change in Control of Interests	4,296	19,906
Fair value of previously held equity interest	2,449	26,433
Total consideration	$ 407,705	$ 1,063,681

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages.

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In a business combination achieved in stages, this element represents the amount of gain recognized by the entity as a result of remeasuring to fair value the equity interest in the acquiree it held before the business combination.

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Amount of increase in noncontrolling interest from subsidiary issuance of equity interests to noncontrolling interest holders.

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The value of the noncash (or part noncash) consideration given (for example, liability, equity) in a transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of a transaction not resulting in cash receipts or cash payments in the period.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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