Acquisitions: (Details 2) (USD $) In Thousands, unless otherwise specified			0 Months Ended
Mar. 31, 2013	Dec. 31, 2012	Oct. 03, 2012 FlatIron Crossing	Oct. 26, 2012 Arrowhead Towne Center
Reconciliation of the purchase price to the fair value of the acquired net assets
Purchase price			$ 310,397	$ 144,400
Less debt assumed			(114,497)	(75,375)
Carrying value of investment	945,935	974,258	33,382	23,597
Remeasurement gain			84,227	115,729
Less prior gain deferral			(26,067)
Fair value of acquired net assets (at 100% ownership)			$ 287,442	$ 208,351
Ownership interest at completion of acquisition (as a percent)			100.00%	100.00%

The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition.

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Percentage of voting equity interests acquired in the business combination.

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Income (expense) and gain (loss) recognized from the settlement of a preexisting relationship between the acquirer and the acquiree.

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The total purchase price of the acquired entity. This includes cash paid to equity interest holders of the acquired entity, fair value of debt and equity securities issued to equity holders of the acquired entity, and transaction costs paid to third parties to consummate the acquisition.

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In a business combination achieved in stages, this element represents the amount of net gain (loss) 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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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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The amount of debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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