Fair value measurements (Tables)

12 Months Ended

Dec. 31, 2013

Fair Value Disclosures [Abstract]

Schedule of fair value of assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy

The following tables set forth the assets and liabilities that we measure at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2013 and 2012 (in thousands):

			December 31, 2013
Description	Total		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Assets:
Available-for-sale securities	$	4,469	$	4,469	$	—	$	—
Interest rate swap agreements	$	2,870	$	—	$	2,870	$	—
Liabilities:
Interest rate swap agreements	$	6,191	$	—	$	6,191	$	—

			December 31, 2012
Description	Total		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Assets:
Available-for-sale securities	$	2,709	$	2,709	$	—	$	—
Liabilities:
Interest rate swap agreements	$	20,661	$	—	$	20,661	$	—

Schedule of the book and fair values of our marketable securities, interest rate swap agreements, secured notes payable, unsecured senior notes payable, unsecured senior line of credit, and unsecured senior bank term loan

As of December 31, 2013 and 2012, the book and fair values of our marketable equity securities, interest rate swap agreements, secured notes payable, unsecured senior notes payable, unsecured senior line of credit, and unsecured senior bank term loans were as follows (in thousands):

	December 31, 2013				December 31, 2012
	Book Value		Fair Value		Book Value		Fair Value
Assets:
Marketable equity securities	$	4,469	$	4,469	$	2,709	$	2,709
Interest rate swap agreements	$	2,870	$	2,870	$	—	$	—
Liabilities:
Interest rate swap agreements	$	6,191	$	6,191	$	20,661	$	20,661
Secured notes payable	$	708,831	$	736,772	$	716,144	$	788,455
Unsecured senior notes payable	$	1,048,230	$	1,043,125	$	549,805	$	593,350
Unsecured senior line of credit	$	204,000	$	193,714	$	566,000	$	567,196
Unsecured senior bank term loans	$	1,100,000	$	1,099,897	$	1,350,000	$	1,405,124