Interest rate swap agreements (Tables)

3 Months Ended

Mar. 31, 2015

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Outstanding interest rate hedge agreements designated as cash flow hedges of interest rate risk

We had the following outstanding interest rate swap agreements that were designated as cash flow hedges of interest rate risk as of March 31, 2015 (dollars in thousands):

		Number of Contracts	Weighted Average Interest Pay Rate (1)	Fair Value as of 3/31/15			Notional Amount in Effect as of
Effective Date	Maturity Date						3/31/15		12/31/15		12/31/16
December 31, 2014	March 31, 2016	3	0.53%	$	(926	)	$	500,000	$	500,000	$	—
March 31, 2015	March 31, 2016	7	0.42%	(362		)	450,000		450,000		—
March 31, 2016	March 31, 2017	5	1.35%	(2,129		)	—		—		600,000
Total				$	(3,417	)	$	950,000	$	950,000	$	600,000

(1) In addition to the interest pay rate for each swap agreement, interest is payable at an applicable margin for borrowings outstanding as of March 31, 2015. Borrowings under our unsecured senior bank term loans include an applicable margin of 1.20% and borrowings outstanding under our unsecured senior line of credit include an applicable margin of 1.10%.

During April 2015, we executed additional interest rate swap agreements that were designated as cash flow hedges of interest rate risk (dollars in thousands):

		Number of Contracts	Weighted Average Interest Pay Rate (1)	Fair Value as of 3/31/15	Notional Amount in Effect as of
Effective Date	Maturity Date				3/31/15		12/31/15		12/31/16
March 31, 2016	March 31, 2017	4	0.93%	N/A	$	—	$	—	$	200,000

(1) In addition to the interest pay rate for each swap agreement, interest is payable at an applicable margin for borrowings outstanding as of March 31, 2015. Borrowings under our unsecured senior bank term loans include an applicable margin of 1.20% and borrowings outstanding under our unsecured senior line of credit include an applicable margin of 1.10%.