Noncontrolling Interest Represented By Preferred Operating Partnership Units - (Details)				1 Months Ended		3 Months Ended								12 Months Ended
	Apr. 18, 2017	Jun. 15, 2016	Jun. 25, 2007 shares	Dec. 31, 2014 USD ($)	Oct. 31, 2014 USD ($) shares	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) shares	Jun. 30, 2017 USD ($) shares	Mar. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Sep. 30, 2016 USD ($) shares	Jun. 30, 2016 USD ($) shares	Mar. 31, 2016 USD ($) shares	Dec. 31, 2017 USD ($) shares $ / shares	Dec. 31, 2016 USD ($) shares	Jun. 30, 2007 USD ($)
Noncontrolling Interest [Line Items]
Loan to holders of preferred OP units						$ 120,230,000				$ 120,230,000				$ 120,230,000	$ 120,230,000
Number of OP Units Issued (in shares) | shares						64,708	25,520	272,400	0	563,819	0	2,215,231	0	362,628	2,779,050
Value of OP Units Issued						$ 5,618,000	$ 2,000,000	$ 6,810,000	$ 0	$ 17,998,000	$ 0	$ 56,237,000	$ 0	$ 14,428,000	$ 74,235,000
Series A Participating Redeemable Preferred Units | Holders Of Series A Preferred Operating Partnership Units
Noncontrolling Interest [Line Items]
Loan to holders of preferred OP units						$ 100,000,000								$ 100,000,000
Note receivable interest rate (as a percent)	2.13%		4.85%
Additional units redeemed | shares			0
Series D Redeemable Preferred Units | Operating Partnership
Noncontrolling Interest [Line Items]
Number of OP Units Issued (in shares) | shares														446,420	2,687,711
Value of OP Units Issued														$ 11,161,000	$ 67,193,000
Series A Units | Series A Participating Redeemable Preferred Units | Operating Partnership
Noncontrolling Interest [Line Items]
Preferred units outstanding (in units) | shares						875,480								875,480
Fixed priority return on preferred OP units, amount					$ 101,700,000											$ 101,700,000
Fixed priority return on preferred OP units, stated return rate (as a percent)	2.25%	5.00%
Fixed priority return on preferred OP units, liquidation value																$ 115,000,000
Series A Units | Series A Participating Redeemable Preferred Units | Holders Of Series A Preferred Operating Partnership Units
Noncontrolling Interest [Line Items]
Maximum number of preferred OP units converted prior to the maturity date of the loan (in shares) | shares					114,500
Series B Units | Series B Redeemable Preferred Units
Noncontrolling Interest [Line Items]
Liquidation value (in dollars per share) | $ / shares						$ 25								$ 25
Fixed liquidation value						$ 41,902,000								$ 41,902,000
Annual rate of return (as a percent)														6.00%
Series B Units | Series B Redeemable Preferred Units | Operating Partnership
Noncontrolling Interest [Line Items]
Preferred units outstanding (in units) | shares						1,676,087								1,676,087
Series C Units | Series C Convertible Redeemable Preferred Units
Noncontrolling Interest [Line Items]
Loan to holders of preferred OP units				$ 20,230,000
Note receivable interest rate (as a percent)				5.00%
Liquidation value (in dollars per share) | $ / shares						$ 42.1								$ 42.1
Fixed liquidation value						$ 29,639,000								$ 29,639,000
Quarterly distribution per preferred OP unit payable above quarterly distribution for common OP Unit (in dollars per share) | $ / shares														$ 0.18
Basis for determining fixed quarterly distribution in year 5, period before fifth anniversary														12 months
Period from date of issuance after which preferred OP units will become redeemable at the option of the holder														1 year
Period from date of issuance after which preferred OP units will become convertible into common OP units at the option of the holder														1 year
Preferred OP units conversion ratio (in units) | shares														0.9145
Series C Units | Series C Convertible Redeemable Preferred Units | Operating Partnership
Noncontrolling Interest [Line Items]
Preferred units outstanding (in units) | shares						704,016								704,016
Series D Units | Series D Redeemable Preferred Units
Noncontrolling Interest [Line Items]
Liquidation value (in dollars per share) | $ / shares						$ 25								$ 25
Fixed liquidation value						$ 92,064,000								$ 92,064,000
Series D Units | Series D Redeemable Preferred Units | Minimum
Noncontrolling Interest [Line Items]
Annual rate of return (as a percent)														3.00%
Series D Units | Series D Redeemable Preferred Units | Maximum
Noncontrolling Interest [Line Items]
Annual rate of return (as a percent)														5.00%
Series D Units | Series D Redeemable Preferred Units | Operating Partnership
Noncontrolling Interest [Line Items]
Preferred units outstanding (in units) | shares						3,682,521								3,682,521