Capital and Financing Transactions - Interest Rate Swap (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended		6 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 12, 2013	Jun. 28, 2013	Jun. 27, 2013	Feb. 10, 2012	Sep. 30, 2014	Apr. 01, 2014	Mar. 25, 2013	Aug. 01, 2013	Apr. 08, 2014	May 31, 2013
Derivative [Line Items]
Outstanding balance	$ 481,500,000				$ 303,000,000				$ 481,500,000	$ 303,000,000
Interest expense	17,515,000	16,543,000	16,793,000	15,244,000	12,610,000	11,521,000	11,162,000	10,329,000	66,095,000	45,622,000	34,352,000
Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Gain (loss) on interest rate cash flow hedge, ineffectiveness									32,000	127,000
Interest rate cash flow hedge gain (loss) to be reclassified near year	6,900,000								6,900,000
Accelerated gain (loss) reclassification from accumulated OCI into income									180,000
Unsecured Term Loan $120 million
Derivative [Line Items]
Outstanding balance					120,000,000					120,000,000
Interest rate												3.30%
Mortgage notes payable																	120,000,000.0
Working Capital Revolving Credit Facility
Derivative [Line Items]
Outstanding balance	0								0
Interest rate	1.70%								1.70%
Account payable and other liabilities | Swap 12
Derivative [Line Items]
Notional amount	120,000,000								120,000,000
Derivative interest rate (in percent)	1.6075%								1.6075%
Tampa Fund II Assets
Derivative [Line Items]
Ownership percentage of noncontrolling interest																		70.00%
London Interbank Offered Rate (LIBOR) | Working Capital Revolving Credit Facility
Derivative [Line Items]
LIBOR rate period fixed												1.60%
Term loan facility swap terms												5 years
Hayden Ferry II Original Mortgage | Hayden Ferry Lakeside II
Derivative [Line Items]
Quarterly principal payment													625,000	625,000
Fixed base rate of variable interest rate													1.50%
Hayden Ferry II Modified Mortgage | Hayden Ferry Lakeside II
Derivative [Line Items]
Notional amount																			625,000
Fixed base rate of variable interest rate																			1.70%
Minimum
Derivative [Line Items]
Basis spread on variable rate (in percent)															2.50%
Minimum | Hayden Ferry II Modified Mortgage | London Interbank Offered Rate (LIBOR) | Hayden Ferry Lakeside II
Derivative [Line Items]
Basis spread on variable rate (in percent)													2.50%
Maximum
Derivative [Line Items]
Basis spread on variable rate (in percent)															3.50%
Maximum | Hayden Ferry II Modified Mortgage | London Interbank Offered Rate (LIBOR) | Hayden Ferry Lakeside II
Derivative [Line Items]
Basis spread on variable rate (in percent)													3.50%
Interest Rate Swap
Derivative [Line Items]
Notional amount																				100,000,000.0
Derivative interest rate (in percent)																					3.30%
Derivative amount terminated																				33,900,000.0
Interest expense			121,000
Interest Rate Swap | Fund II Assets
Derivative [Line Items]
Number of interest rate derivatives held																		2
Notional amount																		34,600,000.0
Interest Rate Swap, 3.3%
Derivative [Line Items]
Notional amount																					13,500,000.0
Interest Rate Swap, 1.6%
Derivative [Line Items]
Notional amount												120,000,000.0
Interest Rate Swap, 1.6% | Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Notional amount												120,000,000.0
Derivative interest rate (in percent)												1.60%
Interest Rate Swap, 0.7% | Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Notional amount																	125,000,000.0
Derivative interest rate (in percent)																	0.70%
Number of derivative instrument held																	2
Interest Rate Swap, 1.7% | Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Notional amount																	5,000,000.0
Derivative interest rate (in percent)																	1.70%
Interest Rate Swap, 2.6% | Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Notional amount																	100,000,000.0
Derivative interest rate (in percent)																	2.60%
Unsecured Debt | Unsecured Term Loan $125 million
Derivative [Line Items]
Mortgage notes payable		$ 125,000,000.0														$ 125,000,000.0
Term of debt instrument																5 years
Unsecured Debt | Seven-year Term Loan
Derivative [Line Items]
Term of debt instrument																	7 years
Period end interest rate (in percent)																	4.31%
Unsecured Debt | Seven-year Term Loan | London Interbank Offered Rate (LIBOR)
Derivative [Line Items]
Interest rate during the period (in percent)																	1.75%
Unsecured Debt | Minimum | Seven-year Term Loan | London Interbank Offered Rate (LIBOR)
Derivative [Line Items]
Basis spread on variable rate (in percent)																	1.75%
Unsecured Debt | Maximum | Seven-year Term Loan | London Interbank Offered Rate (LIBOR)
Derivative [Line Items]
Basis spread on variable rate (in percent)																	2.30%