Noncontrolling Interest Represented by Preferred Operating Partnership Units - Additional Information (Details) $ / shares in Units, $ in Thousands										1 Months Ended	3 Months Ended		6 Months Ended
	Nov. 04, 2016 USD ($) shares	May 21, 2016 USD ($) store shares	Oct. 03, 2014 USD ($) shares	Apr. 03, 2014 USD ($) store shares	Nov. 19, 2013 store	Sep. 26, 2013 USD ($) store shares	Aug. 29, 2013 store	Jun. 25, 2007 USD ($) shares	Jun. 15, 2007 store shares	Dec. 31, 2014 USD ($) store shares	Mar. 31, 2017 USD ($) shares store $ / shares	Mar. 31, 2016 USD ($)	May 31, 2014 USD ($) store shares	Dec. 31, 2016 USD ($)	Jun. 15, 2016 USD ($)
Noncontrolling Interest [Line Items]
Note receivable from noncontrolling interest represented by Preferred Operating Partnership units											$ 120,230			$ 120,230
Redemption of Operating Partnership units held by noncontrolling interests											$ 1,754	$ 0
Number of stores acquired | store											2
Series B Redeemable Preferred Units [Member] | Series B Units [Member]
Noncontrolling Interest [Line Items]
Liquidation value (in dollars per share) | $ / shares											$ 25
Fixed liquidation value											$ 41,902
Annual rate of return (as a percent)											6.00%
Series B Redeemable Preferred Units [Member] | Series B Units [Member] | Georgia, 1 Property Acquired 4/3/2014 [Member]
Noncontrolling Interest [Line Items]
Preferred units issued as part of acquisition (in units) | shares				333,360
Preferred units issued as part of acquisition				$ 8,334
Series C Convertible Redeemable Preferred Units [Member] | California, Properties Acquired December 2013 [Member]
Noncontrolling Interest [Line Items]
Number of stores acquired | store					12
Ownership interests in five stores through joint ventures prior to the acquisition													35.00%
Number of stores in which ownership interest was held prior to acquisition of remaining properties | store													5
Ownership interest in one store through joint ventures prior to the acquisition													40.00%
Number of stores in which ownership interest was held prior to acquisition | store													1
Series C Convertible Redeemable Preferred Units [Member] | Series C Units [Member]
Noncontrolling Interest [Line Items]
Note receivable from noncontrolling interest represented by Preferred Operating Partnership units										$ 20,230
Note receivable interest rate										5.00%
Liquidation value (in dollars per share) | $ / shares											$ 42.10
Fixed liquidation value											$ 29,639
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
Note receivable maturity date										Dec. 15, 2024
Series D Redeemable Preferred Units [Member] | Series D Units [Member]
Noncontrolling Interest [Line Items]
Liquidation value (in dollars per share) | $ / shares											$ 25.00
Fixed liquidation value											$ 80,903
Series D Redeemable Preferred Units [Member] | D-1 Units[Member] | Minimum [Member]
Noncontrolling Interest [Line Items]
Annual rate of return (as a percent)											3.50%
Series D Redeemable Preferred Units [Member] | D-1 Units[Member] | Maximum [Member]
Noncontrolling Interest [Line Items]
Annual rate of return (as a percent)											5.00%
Operating Partnership [Member] | Illinois Property Acquired 5/21/2016 [Member]
Noncontrolling Interest [Line Items]
Number of stores acquired | store		4
Operating Partnership [Member] | Series A Participating Redeemable Preferred Units [Member]
Noncontrolling Interest [Line Items]
Number of stores acquired | store									10
Operating Partnership [Member] | Series A Participating Redeemable Preferred Units [Member] | Series A Units [Member]
Noncontrolling Interest [Line Items]
Preferred units issued as part of acquisition (in units) | shares									989,980
Fixed priority return on preferred OP units, amount															$ 115,000
Fixed priority return on preferred OP units, stated return rate											5.00%
Fixed priority return on preferred OP units, liquidation value											$ 115,000
Operating Partnership [Member] | Series B Redeemable Preferred Units [Member] | Georgia, 1 Property Acquired 4/3/2014 [Member]
Noncontrolling Interest [Line Items]
Number of stores acquired | store				1
Cash portion of payment for acquisition				$ 15,158
Operating Partnership [Member] | Series B Redeemable Preferred Units [Member] | California, 20 Properties Acquired 2013-September [Member]
Noncontrolling Interest [Line Items]
Number of stores acquired | store						1	19
Cash portion of payment for acquisition						$ 100,876
Number of stores acquired as part of portfolio acquisition | store							20
Debt assumed						$ 98,960
Number of common units issued as part of acquisition (in units) | shares						1,448,108
OP units issued as part of the acquisition						$ 62,341
Operating Partnership [Member] | Series B Redeemable Preferred Units [Member] | Series B Units [Member] | California, 20 Properties Acquired 2013-September [Member]
Noncontrolling Interest [Line Items]
Preferred units issued as part of acquisition (in units) | shares						1,342,727
Preferred units issued as part of acquisition						$ 33,568
Operating Partnership [Member] | Series C Convertible Redeemable Preferred Units [Member] | California, Properties Acquired December 2013 [Member]
Noncontrolling Interest [Line Items]
Cash portion of payment for acquisition													$ 45,722
Debt assumed													$ 37,532
Number of stores acquired | store													6
Operating Partnership [Member] | Series C Convertible Redeemable Preferred Units [Member] | Series C Units [Member] | California, Properties Acquired December 2013 [Member]
Noncontrolling Interest [Line Items]
Preferred units issued as part of acquisition (in units) | shares													704,016
Preferred units issued as part of acquisition													$ 30,960
Operating Partnership [Member] | Series D Redeemable Preferred Units [Member] | Self Storage Facility in Florida [Member]
Noncontrolling Interest [Line Items]
Number of stores acquired | store										1
Cash portion of payment for acquisition										$ 5,621
Operating Partnership [Member] | Series D Redeemable Preferred Units [Member] | D-4 Preferred Units [Member] | Illinois Property Acquired 5/21/2016 [Member]
Noncontrolling Interest [Line Items]
Number of OP units issued for store acquisition (in units) | shares	486,244
Operating Partnership units issued	$ 12,156
Operating Partnership [Member] | Series D Redeemable Preferred Units [Member] | D-3 Units [Member] | Illinois Property Acquired 5/21/2016 [Member]
Noncontrolling Interest [Line Items]
Number of OP units issued for store acquisition (in units) | shares		2,201,467
Operating Partnership units issued		$ 55,037
Operating Partnership [Member] | Series D Redeemable Preferred Units [Member] | Series D Units [Member] | Self Storage Facility in Florida [Member]
Noncontrolling Interest [Line Items]
Preferred units issued as part of acquisition (in units) | shares										548,390
Preferred units issued as part of acquisition										$ 13,710
Operating Partnership Holders of A Units [Member] | Series A Participating Redeemable Preferred Units [Member]
Noncontrolling Interest [Line Items]
Note receivable from noncontrolling interest represented by Preferred Operating Partnership units								$ 100,000
Note receivable interest rate								4.85%
Maximum number of preferred OP units converted prior to the maturity date of the loan (in units) | shares								114,500
A units redeemed | shares			114,500
Redemption of Operating Partnership units held by noncontrolling interests			$ 4,794
Common shares issued in Preferred Unit redemption (in shares) | shares			280,331
Additional units redeemed (in units) | shares			0