Fair value measurements (Tables)

12 Months Ended

Dec. 31, 2019

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, 2019 and 2018 (in thousands):

			December 31, 2019
Description	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Investments in publicly traded companies	$	318,637	$	318,637	$	—	$	—

			December 31, 2018
Description	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Investments in publicly traded companies	$	184,005	$	184,005	$	—	$	—
Interest rate hedge agreements	$	2,606	$	—	$	2,606	$	—
Liabilities:
Interest rate hedge agreements	$	768	$	—	$	768	$	—

Schedule of the book and fair values

As of December 31, 2019 and 2018, the book and estimated fair values of our secured notes payable, unsecured senior notes payable, unsecured senior line of credit and unsecured senior bank term loan were as follows (in thousands):

	December 31,
	2019				2018
	Book Value		Fair Value		Book Value		Fair Value
Liabilities:
Secured notes payable	$	349,352	$	363,344	$	630,547	$	638,860
Unsecured senior notes payable	$	6,044,127	$	6,571,668	$	4,292,293	$	4,288,335
Unsecured senior line of credit	$	384,000	$	383,928	$	208,000	$	208,106
Unsecured senior bank term loan	$	—	$	—	$	347,415	$	350,240