Acquisitions: Narrative (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 03, 2013	Jul. 22, 2011 sqft	Feb. 29, 2012 sqft	Oct. 03, 2012 sqft	Oct. 26, 2012 sqft	Nov. 28, 2012 sqft	Jan. 31, 2013	Jan. 24, 2013 sqft	Apr. 25, 2013 acre	Oct. 24, 2013	Jun. 04, 2014	Nov. 14, 2014	Oct. 31, 2014	Sep. 17, 2013 sqft	Sep. 16, 2013
Acquisition
Acquisition of properties by assumption of mortgage note payable and other accrued liabilities	$ 1,414,659,000	$ 257,064,000	$ 420,123,000
Deposits paid	0	0	30,000,000
Kings Plaza Shopping Center
Acquisition
Placement of mortgage note on the property				146,000,000
Camelback Colonnade
Acquisition
Property square footage																	619,000
Ownership Percentage																		73.20%
Additional ownership interest (as a percent)																	67.50%
Ownership percentage at completion of acquisition (as a percent)																		100.00%
Fashion Outlets of Niagara
Acquisition
Property square footage					686,000
Purchase price					200,000,000
Fair value of contingent consideration	18,667,000
500 North Michigan Avenue:
Acquisition
Property square footage						326,000
Purchase price						70,925,000
FlatIron Crossing
Acquisition
Property square footage							1,434,000
Purchase price							310,397,000
Purchase price funded by cash payment on acquisition							195,900,000
Acquisition of properties by assumption of mortgage note payable and other accrued liabilities							114,497,000
Additional ownership interest (as a percent)	75.00%						75.00%
Ownership percentage at completion of acquisition (as a percent)							100.00%
Arrowhead Towne Center
Acquisition
Property square footage								1,198,000
Purchase price								144,400,000
Purchase price funded by cash payment on acquisition								69,025,000
Acquisition of properties by assumption of mortgage note payable and other accrued liabilities								75,375,000
Additional ownership interest (as a percent)								33.30%
Ownership percentage at completion of acquisition (as a percent)								100.00%
Kings Plaza
Acquisition
Property square footage									1,191,000
Purchase price									756,000,000
Purchase price funded by cash payment on acquisition									726,000,000
Issuance restricted common stock									30,000,000
Face amount of debt									500,000,000
Placement of mortgage note on the property									354,000,000
Green Acres Mall
Acquisition
Property square footage											1,790,000
Purchase price											500,000,000
Face amount of debt											325,000,000
Placement of mortgage note on the property										225,000,000	100,000,000
Deposits paid		30,000,000
Purchase price, balance remaining after deposit											470,000,000
Green Acres Adjacent
Acquisition
Property square footage												19
Purchase price												22,577,000
Superstition Springs Land I
Acquisition
Purchase price													46,162,000
Purchase price funded by cash payment on acquisition													23,662,000
Acquisition of properties by assumption of mortgage note payable and other accrued liabilities													22,500,000
Additional ownership interest (as a percent)													33.30%
Ownership percentage at completion of acquisition (as a percent)													100.00%
Cascade Mall
Acquisition
Purchase price														15,233,000
Incremental revenue generated from acquired property	4,458,000
Incremental earnings (loss) of acquired property	380,000
Additional ownership interest (as a percent)														49.00%
Ownership percentage at completion of acquisition (as a percent)													100.00%
PPRLP Queens Portfolio
Acquisition
Purchase price															1,838,886,000
Acquisition of properties by assumption of mortgage note payable and other accrued liabilities															672,109,000
Issuance restricted common stock															1,166,777,000
Incremental revenue generated from acquired property	40,378,000
Incremental earnings (loss) of acquired property	4,285,000
Additional ownership interest (as a percent)															49.00%
Affiliated Entity | Fashion Outlets of Chicago
Acquisition
Property square footage		529,000
Purchase price																69,987,000
Fair value of contingent consideration	10,142,000
Noncontrolling interest adjustment	76,141,000
Purchase price funded by cash payment on acquisition																55,867,000
Acquisition of properties by assumption of mortgage note payable and other accrued liabilities																$ 14,120,000