KW UNSECURED DEBT - Borrowings Under Credit Facilities (Details) - USD ($)				12 Months Ended
	Oct. 20, 2017	Oct. 03, 2017	Dec. 10, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Repayment of lines of credit				$ 500,000,000	$ 125,000,000	$ 220,000,000
Borrowings under lines of credit				800,000,000	125,000,000	$ 95,000,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Debt (excluding loan fees)				$ 1,198,100,000	952,800,000
Revolving Credit Facility [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Fixed charge coverage ratio				3.1
Tangible net worth				$ 1,954,500,000
Secured recourse leverage ratio				0.80%
Liquidity				$ 358,800,000
Consolidated leverage ratio				63.10%
Adjusted secured leverage ratio				37.90%
Recourse leverage ratio				0.65
Debt (excluding loan fees)				$ 300,000,000	$ 0
A&R Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity and debt instrument, face amount		$ 700,000,000
A&R Facility [Member] | Medium-term Notes [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		200,000,000
Proceeds from issuance of debt		$ 200,000,000
A&R Facility [Member] | Medium-term Notes [Member] | LIBOR [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as percent)		1.65%
A&R Facility [Member] | Medium-term Notes [Member] | LIBOR [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as percent)		2.65%
A&R Facility [Member] | Revolving Credit Facility [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 500,000,000
Maturity of extension			1 year
Proceeds from issuance of debt		$ 200,000,000		400,000,000
Maximum consolidated leverage ratio	65.00%
Fixed charge coverage ratio measurement period	12 months
Covenant, percent of new equity offerings	50.00%
Maximum secured recourse leverage multiplier	1.5
Repayments of debt				100,000,000
Maximum amount outstanding during period				550,000,000
Remaining borrowing capacity				400,000,000
A&R Facility [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Fixed charge coverage ratio	1.70
Tangible net worth	$ 1,066,775,300
Liquidity	$ 75,000,000.0
A&R Facility [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Secured recourse leverage ratio	3.50%
Liquidity	$ 300,351,000
Adjusted secured leverage ratio	55.00%
A&R Facility [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | LIBOR [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as percent)		1.75%
A&R Facility [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | LIBOR [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as percent)		2.75%
KW Revolving Facility [Member] | Revolving Credit Facility [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 475,000,000
Average outstanding amount				285,200,000
KW Revolving Facility [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | LIBOR [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as percent)			2.50%
KW Revolving Facility [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] | LIBOR [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate (as percent)			3.00%
KW Revolving Facility [Member] | Revolving Credit Facility [Member] | Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Repayment of lines of credit		$ 350,000,000
Borrowings under lines of credit				400,000,000
Maximum amount outstanding during period				$ 375,000,000