Subsequent Events - Additional Information (Detail)						12 Months Ended
	Feb. 17, 2017 USD ($) building	Feb. 14, 2017 USD ($) ft² extension	Jan. 05, 2017 USD ($) $ / shares shares	Feb. 03, 2015 USD ($) $ / shares	Aug. 19, 2014 USD ($) $ / shares	Dec. 31, 2016 USD ($) ft² building $ / shares shares	Dec. 31, 2015 USD ($) a building $ / shares shares	Dec. 31, 2014 USD ($)	Jun. 11, 2014 USD ($)
Subsequent Event [Line Items]
Common stock share price (in dollars per share) | $ / shares				$ 16	$ 13.50	$ 23.1258756888	$ 16.07
Issuance of common stock, net				$ 176,200,000	$ 221,800,000	$ 183,386,000	$ 175,833,000	$ 221,773,000
Maximum borrowing capacity									$ 600,000,000.0
Payments to Acquire Real Estate						$ 367,621,000	$ 230,599,000	$ 383,662,000
Number of Buildings | building						30	39
Net Rentable Area						3,372,794	2,129,753
Minimum
Subsequent Event [Line Items]
Additional interest						0.20%
Maximum
Subsequent Event [Line Items]
Additional interest						0.30%
LIBOR
Subsequent Event [Line Items]
Basis spread on variable rate						1.00%
Revolving Credit Facility | LIBOR | Minimum
Subsequent Event [Line Items]
Basis spread on variable rate						1.30%
Revolving Credit Facility | LIBOR | Maximum
Subsequent Event [Line Items]
Basis spread on variable rate						1.90%
Line of Credit | 300 Million Credit Facility
Subsequent Event [Line Items]
Maximum borrowing capacity						$ 300,000,000
Subsequent Event
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 550,000,000
Subsequent Event | Eurodollar
Subsequent Event [Line Items]
Basis spread on variable rate		1.00%
Subsequent Event | Base Rate
Subsequent Event [Line Items]
Basis spread on variable rate		0.50%
Subsequent Event | Unsecured Revolving Credit Facility | Minimum
Subsequent Event [Line Items]
Additional interest		0.15%
Commitment Fee Percentage if pricing structure is converted to be based on an investment-grade rating		0.125%
Subsequent Event | Unsecured Revolving Credit Facility | Maximum
Subsequent Event [Line Items]
Additional interest		0.30%
Commitment Fee Percentage if pricing structure is converted to be based on an investment-grade rating		0.30%
Subsequent Event | Unsecured Revolving Credit Facility | LIBOR | Minimum
Subsequent Event [Line Items]
Basis spread on variable rate		1.10%
Basis spread on variable rate if additional investment grade rating is attained		0.825%
Subsequent Event | Unsecured Revolving Credit Facility | LIBOR | Maximum
Subsequent Event [Line Items]
Basis spread on variable rate		1.50%
Basis spread on variable rate if additional investment grade rating is attained		1.55%
Subsequent Event | Unsecured Revolving Credit Facility | Base Rate | Minimum
Subsequent Event [Line Items]
Basis spread on variable rate		0.10%
Basis spread on variable rate if additional investment grade rating is attained		0.00%
Subsequent Event | Unsecured Revolving Credit Facility | Base Rate | Maximum
Subsequent Event [Line Items]
Basis spread on variable rate		0.50%
Basis spread on variable rate if additional investment grade rating is attained		0.55%
Subsequent Event | 100 Million Term Loan [Member] | LIBOR | Minimum
Subsequent Event [Line Items]
Basis spread on variable rate		1.20%
Basis spread on variable rate if additional investment grade rating is attained		0.90%
Subsequent Event | 100 Million Term Loan [Member] | LIBOR | Maximum
Subsequent Event [Line Items]
Basis spread on variable rate		1.70%
Basis spread on variable rate if additional investment grade rating is attained		1.75%
Subsequent Event | 100 Million Term Loan [Member] | Base Rate | Minimum
Subsequent Event [Line Items]
Basis spread on variable rate		0.20%
Basis spread on variable rate if additional investment grade rating is attained		0.00%
Subsequent Event | 100 Million Term Loan [Member] | Base Rate | Maximum
Subsequent Event [Line Items]
Basis spread on variable rate		0.70%
Basis spread on variable rate if additional investment grade rating is attained		0.75%
Subsequent Event | Line of Credit | 450 Million Senior Credit Facility | Unsecured Credit Facility
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 450,000,000
Number of extensions | extension		2
Extension duration period		6 months
Subsequent Event | Line of Credit | Unsecured Revolving Credit Facility | Revolving Credit Facility
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 350,000,000
Subsequent Event | Line of Credit | 100 Million Term Loan [Member] | Term Loan
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 100,000,000
At The Market Equity Offering Program
Subsequent Event [Line Items]
Common Stock, Shares, Issued | shares						402,683	500
Common stock share price (in dollars per share) | $ / shares							$ 14.3
Issuance of common stock, net						$ 9,300,000	$ 0
Proceeds from issuance of common stock, net						$ 9,200,000
At The Market Equity Offering Program | Subsequent Event
Subsequent Event [Line Items]
Common Stock, Shares, Issued | shares			168,685
Common stock share price (in dollars per share) | $ / shares			$ 23.1576488722
Issuance of common stock, net			$ 3,900,000
Proceeds from issuance of common stock, net			$ 3,800,000
28903 Avenue Paine | Subsequent Event
Subsequent Event [Line Items]
Payments to Acquire Real Estate	$ 17,100,000
Number of Buildings | building	1
Net Rentable Area | ft²		111,000