Noncontrolling Interest Represented by Preferred Operating Partnership Units - Additional Information (Details)				1 Months Ended		6 Months Ended
	Apr. 18, 2017	Jun. 15, 2016	Jun. 25, 2007	Dec. 31, 2014 USD ($)	Oct. 31, 2014 shares	Jun. 30, 2018 USD ($) shares $ / shares	Dec. 31, 2017 USD ($)	Jun. 30, 2007 USD ($)
Noncontrolling Interest [Line Items]
Note receivable from noncontrolling interest represented by Preferred Operating Partnership units						$ 119,735,000	$ 120,230,000
Series B Redeemable Preferred Units | Series B Units
Noncontrolling Interest [Line Items]
Liquidation value (in dollars per share) | $ / shares						$ 25
Fixed liquidation value						$ 41,902,000
Annual rate of return (as a percent)						6.00%
Series C Convertible Redeemable Preferred Units | Series C Units
Noncontrolling Interest [Line Items]
Note receivable from noncontrolling interest represented by Preferred Operating Partnership units				$ 20,230,000		$ 19,735,000	$ 20,230,000
Note receivable interest rate				5.00%
Liquidation value (in dollars per share) | $ / shares						$ 42.1
Fixed liquidation value						$ 29,639,000
Quarterly distribution per preferred OP unit payable above quarterly distribution for common OP Unit (in dollars per share) | $ / shares						$ 0.18
Number of months immediately preceding the fifth anniversary of issuance for which distribution is payable						12 months
Period from date of issuance after which preferred OP units will become redeemable at the option of the holder						1 year
Preferred OP units conversion ratio | shares						0.9145
Series D Redeemable Preferred Units | Series D Units
Noncontrolling Interest [Line Items]
Fixed liquidation value						$ 25,000
Series D Redeemable Preferred Units | Series D Units | Minimum
Noncontrolling Interest [Line Items]
Annual rate of return (as a percent)						5.00%
Series D Redeemable Preferred Units | Series D Units | Maximum
Noncontrolling Interest [Line Items]
Annual rate of return (as a percent)						9206400.00%
Operating Partnership | Series A Participating Redeemable Preferred Units | Series A Units
Noncontrolling Interest [Line Items]
Preferred units outstanding (in shares) | shares						875,480
Fixed priority return on preferred OP units, amount								$ 101,700,000
Fixed priority return on preferred OP units, stated return rate	2.25%	5.00%
Fixed priority return on preferred OP units, liquidation value								$ 115,000,000
Operating Partnership | Series B Redeemable Preferred Units | Series B Units
Noncontrolling Interest [Line Items]
Preferred units outstanding (in shares) | shares						1,676,087
Operating Partnership | Series C Convertible Redeemable Preferred Units | Series C Units
Noncontrolling Interest [Line Items]
Preferred units outstanding (in shares) | shares						704,016
Operating Partnership | Series D Convertible Redeemable Preferred Units | Series D Units
Noncontrolling Interest [Line Items]
Preferred units outstanding (in shares) | shares						3,682,521
Operating Partnership Holders of A Units | Series A Participating Redeemable Preferred Units
Noncontrolling Interest [Line Items]
Note receivable from noncontrolling interest represented by Preferred Operating Partnership units						$ 100,000,000
Note receivable interest rate	2.13%		4.85%
Operating Partnership Holders of A Units | Series A Participating Redeemable Preferred Units | Series A Units
Noncontrolling Interest [Line Items]
Maximum number of preferred OP units converted prior to the maturity date of the loan (in units) | shares					114,500