Subsequent Events - Narrative (Details) $ / shares in Units, $ in Millions								1 Months Ended		12 Months Ended
	Feb. 15, 2017 $ / shares	Jan. 31, 2017 USD ($) ft² building	Jan. 12, 2017 $ / shares	Oct. 10, 2016 $ / shares	Jul. 11, 2016 $ / shares	Apr. 15, 2016 $ / shares	Jan. 26, 2016 $ / shares	Feb. 28, 2017 USD ($)	Jan. 31, 2013 building	Dec. 31, 2016 building	Dec. 31, 2015 building	Dec. 31, 2014 ft² building	Mar. 31, 2014 ft²
Subsequent Event [Line Items]
Number of buildings sold | building									18
Property square feet | ft²													5,641,450
Series D
Subsequent Event [Line Items]
Dividend declared (in dollars per share) | $ / shares				$ 0.40625	$ 0.40625	$ 0.40625	$ 0.40625
Disposed of by Sale
Subsequent Event [Line Items]
Number of buildings sold | building										62	135	43
Property square feet | ft²												2,784,098
Subsequent event | Series D
Subsequent Event [Line Items]
Dividend declared (in dollars per share) | $ / shares			$ 0.40625
Dividends paid (in dollars per share) | $ / shares	$ 0.40625
Subsequent event | Disposed of by Sale
Subsequent Event [Line Items]
Number of buildings sold | building		1
Property square feet | ft²		589,380
Gross proceeds from sale of real estate anticipated | $		$ 60.1
US Treasury Notes | Subsequent event
Subsequent Event [Line Items]
Purchase of US Treasury Notes | $								$ 100.0
Treasury notes, term								2 years
Treasury notes, coupon rate								1.125%
Treasury notes, weighted average yield								1.227%