Notes Payable (Credit Facility Table) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Less than or equal to 30% [Member]
Line of Credit Facility [Line Items]
Annual Facility Fee (percent)	0.15%
Greater than 30% but less than or equal to 35% [Member]
Line of Credit Facility [Line Items]
Annual Facility Fee (percent)	0.20%
Greater than 35% but less than or equal to 40% [Member]
Line of Credit Facility [Line Items]
Annual Facility Fee (percent)	0.20%
Greater than 40% but less than or equal to 45% [Member]
Line of Credit Facility [Line Items]
Annual Facility Fee (percent)	0.20%
Greater than 45% but less than or equal to 50% [Member]
Line of Credit Facility [Line Items]
Annual Facility Fee (percent)	0.25%
Greater than 50% [Member]
Line of Credit Facility [Line Items]
Annual Facility Fee (percent)	0.30%
Base rate [Member] | Less than or equal to 30% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.10%
Base rate [Member] | Greater than 30% but less than or equal to 35% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.10%
Base rate [Member] | Greater than 35% but less than or equal to 40% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.15%
Base rate [Member] | Greater than 40% but less than or equal to 45% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.20%
Base rate [Member] | Greater than 45% but less than or equal to 50% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.20%
Base rate [Member] | Greater than 50% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.45%
LIBOR [Member] | Less than or equal to 30% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.10%
LIBOR [Member] | Greater than 30% but less than or equal to 35% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.10%
LIBOR [Member] | Greater than 35% but less than or equal to 40% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.15%
LIBOR [Member] | Greater than 40% but less than or equal to 45% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.20%
LIBOR [Member] | Greater than 45% but less than or equal to 50% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.20%
LIBOR [Member] | Greater than 50% [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.45%
Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 500
Leverage ratio, upper limit (percent)	60.00%
Line of Credit [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.10%