Notes Payable - Summary of Notes Payable (Detail)		9 Months Ended	12 Months Ended
	Jan. 14, 2016	Sep. 30, 2016 USD ($) loan	Dec. 31, 2016 USD ($) property extension swap	May 12, 2016 USD ($)	Feb. 24, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 11, 2014 USD ($)
Debt Instrument [Line Items]
Principal amount			$ 502,476,000			$ 418,698,000
Less: unamortized discount and deferred loan costs			(2,292,000)			(544,000)
Notes payable			$ 500,184,000			418,154,000
Maximum borrowing capacity							$ 600,000,000.0
Number of extensions | extension			1
225 Million Term Loan Facility
Debt Instrument [Line Items]
Debt Instrument, Number Of Additional Incremental Loans | loan		1
Maximum borrowing capacity		$ 100,000,000
Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Current borrowing capacity			$ 200,000,000.0
Term Loan One
Debt Instrument [Line Items]
Notes payable			$ 60,000,000
Description of variable rate basis			LIBOR
Term Loan two
Debt Instrument [Line Items]
Description of variable rate basis			LIBOR
Term Loan Facility
Debt Instrument [Line Items]
Description of variable rate basis			LIBOR
LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate			1.00%
LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Principal amount			$ 0			140,500,000
Less: unamortized discount and deferred loan costs			$ 0			0
Maturity date			Jun. 11, 2018
Effective Interest Rate			2.32%
LIBOR | 225 Million Term Loan Facility
Debt Instrument [Line Items]
Principal amount			$ 225,000,000			0
Less: unamortized discount and deferred loan costs			$ 1,680,000			0
Maturity date			Jan. 14, 2023
Effective Interest Rate			2.65%
LIBOR | Term Loan One
Debt Instrument [Line Items]
Principal amount			$ 59,674,000			60,000,000
Less: unamortized discount and deferred loan costs			$ 204,000			283,000
Maturity date			Aug. 01, 2019
Effective Interest Rate			3.95%
Basis spread on variable rate			1.90%
Extension period			1 year
Number of extensions | extension			1
Number of properties securing loan | property			6
Number of derivative instruments | swap			2
LIBOR | Term Loan two
Debt Instrument [Line Items]
Basis spread on variable rate			1.75%
Number of properties securing loan | property			8
LIBOR | Term Loan Facility
Debt Instrument [Line Items]
Principal amount			$ 100,000,000			100,000,000
Less: unamortized discount and deferred loan costs			$ 0			0
Maturity date			Jun. 11, 2019
Effective Interest Rate			3.40%
Basis spread on variable rate			1.50%
RIF V - Glendale Commerce Center, LLC
Debt Instrument [Line Items]
Description of variable rate basis			LIBOR
RIF V - Glendale Commerce Center, LLC | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate			2.00%
Unsecured Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Extension period			1 year
Number of extensions | extension			1
Unsecured Credit Facility | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate			1.55%
Fixed Rate Debt | 60 Million Term Loan Facility [Member]
Debt Instrument [Line Items]
Amortization period			30 years
Fixed Rate Debt | LIBOR | 60 Million Term Loan Facility [Member]
Debt Instrument [Line Items]
Number of derivative instruments | swap			2
Fixed Rate Debt | Gilbert La Palma [Member]
Debt Instrument [Line Items]
Amortization period			20 years
Fixed Rate Debt | 1065 Walnut Street [Member]
Debt Instrument [Line Items]
Amortization period			25 years
Fixed Rate Debt | Gilbert Street La Palma Avenue
Debt Instrument [Line Items]
Principal amount			$ 2,909,000			3,044,000
Less: unamortized discount and deferred loan costs			$ 145,000			153,000
Maturity date			Mar. 01, 2031
Fixed interest rate			5.125%
Effective Interest Rate			5.39%
Amortization period			20 years
Fixed Rate Debt | 9401 De Soto Ave
Debt Instrument [Line Items]
Principal amount			$ 5,182,000			5,299,000
Less: unamortized discount and deferred loan costs			$ (180,000)			(303,000)
Maturity date			Apr. 01, 2018
Fixed interest rate			5.95%
Effective Interest Rate			3.50%
Amortization period			30 years
Extension period			5 years
Number of extensions | extension			1
Fixed Rate Debt | 1065 E. Walnut Street
Debt Instrument [Line Items]
Principal amount			$ 9,711,000			9,855,000
Less: unamortized discount and deferred loan costs			$ (192,000)			(292,000)
Maturity date			Feb. 01, 2019
Fixed interest rate			4.55%
Effective Interest Rate			3.54%
Extension period			5 years
Fixed Rate Debt | 12907 Imperial Highway and 1065 E. Walnut Street
Debt Instrument [Line Items]
Amortization period			30 years
Senior Notes
Debt Instrument [Line Items]
Principal amount			$ 100,000,000			100,000,000
Less: unamortized discount and deferred loan costs			$ 635,000			$ 703,000
Maturity date			Aug. 06, 2025
Fixed interest rate			4.29%
Effective Interest Rate			4.36%
Line of Credit | 225 Million Term Loan Facility | Term Loan
Debt Instrument [Line Items]
Principal amount		$ 225,000,000
Line of Credit | LIBOR | 225 Million Term Loan Facility | Term Loan
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Interest Rate Swap
Debt Instrument [Line Items]
Interest rate swap agreement, notional amount				$ 100,000,000	$ 125,000,000
Minimum
Debt Instrument [Line Items]
Additional interest			0.20%
Minimum | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate			1.30%
Minimum | LIBOR | Term Loan Facility
Debt Instrument [Line Items]
Additional interest			0.20%
Line of credit facility, amount outstanding			$ 100,000,000
Minimum | Line of Credit | LIBOR | 225 Million Term Loan Facility | Term Loan
Debt Instrument [Line Items]
Basis spread on variable rate		1.50%	1.50%
Maximum
Debt Instrument [Line Items]
Additional interest			0.30%
Maximum | LIBOR | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate			1.90%
Maximum | LIBOR | Term Loan Facility
Debt Instrument [Line Items]
Additional interest			0.30%
Line of credit facility, amount outstanding			$ 100,000,000
Maximum | Line of Credit | LIBOR | 225 Million Term Loan Facility | Term Loan
Debt Instrument [Line Items]
Basis spread on variable rate		2.25%	2.25%