Debt (Details) (USD $)					0 Months Ended		12 Months Ended					12 Months Ended						0 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 SV1 - Mortgage loan	Dec. 31, 2012 SV1 - Mortgage loan	Jan. 31, 2014 SV1 - Mortgage loan Subsequent event	Jun. 28, 2013 Revolving credit facility	Dec. 31, 2013 Revolving credit facility item	Dec. 31, 2012 Revolving credit facility	Dec. 31, 2013 Revolving credit facility Operating partnership	Dec. 31, 2013 Revolving credit facility Minimum	Dec. 31, 2013 Revolving credit facility Maximum	Dec. 31, 2013 Revolving credit facility LIBOR Operating partnership	Dec. 31, 2013 Revolving credit facility LIBOR Minimum Operating partnership	Dec. 31, 2013 Revolving credit facility LIBOR Maximum Operating partnership	Dec. 31, 2013 Revolving credit facility Base rate Operating partnership	Dec. 31, 2013 Revolving credit facility Base rate Minimum Operating partnership	Dec. 31, 2013 Revolving credit facility Base rate Maximum Operating partnership	Jan. 31, 2014 Senior Unsecured Term Loan Subsequent event	Feb. 03, 2014 Senior Unsecured Term Loan Subsequent event Interest rate swap	Jan. 31, 2014 Senior Unsecured Term Loan Subsequent event Operating partnership	Feb. 03, 2014 Senior Unsecured Term Loan Subsequent event LIBOR Interest rate swap	Jan. 31, 2014 Senior Unsecured Term Loan Subsequent event LIBOR Operating partnership	Jan. 31, 2014 Senior Unsecured Term Loan Subsequent event LIBOR Minimum Operating partnership	Jan. 31, 2014 Senior Unsecured Term Loan Subsequent event LIBOR Maximum Operating partnership	Jun. 28, 2013 Prior facility	Jan. 02, 2013 Prior facility
Debt
Interest rate as of reporting date (as a percent)			3.67%	3.71%			2.17%	2.46%
Total principal outstanding	$ 232,500,000	$ 59,750,000	$ 58,250,000	$ 59,750,000			$ 174,250,000
Commitment under the credit agreement						355,000,000	405,000,000		500,000,000									100,000,000		200,000,000					355,000,000	225,000,000
Term of loan facility																		5 years
Number of options available for extensions							1
Extension fee (as a percent)							0.25%
Total increase in commitment under accordion feature						50,000,000														100,000,000
Reference rate												LIBOR			base rate						one month LIBOR	LIBOR
Interest rate margin (as a percent)													2.00%	2.75%		1.00%	1.75%		3.23%				1.75%	2.65%
Notional amount of interest rate derivatives																			100,000,000
Amount borrowed under term loan or revolving credit facility																			100,000,000
Term of derivative																			5 years
Repayment of loan facility					58,300,000
Amount available for borrowing under the facility							222,400,000
Outstanding borrowings							$ 174,300,000
Leverage ratio, Covenant (as a percent)											60.00%
Leverage ratio (as a percent)							15.50%
Secured debt ratio, Covenant (as a percent)											4.00%
Secured debt ratio (as a percent)							3.70%
Fixed charge coverage ratio, Covenant										1.75
Fixed charge coverage ratio										7.20%
Unhedged variable rate debt ratio, Covenant (as a percent)											30.00%
Unhedged variable rate debt ratio (as a percent)							14.90%