Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts		$ 6,855
Common Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 275,000; shares issued and outstanding: 128,333 in 2018 and 128,447 in 2017
Common shares of beneficial interest; par value	$ 0.03	$ 0.03
Common shares of beneficial interest, shares authorized (in shares)	275,000,000	275,000,000
Common shares of beneficial interest, shares issued (in shares)	128,702,000	128,333,000
Common shares of beneficial interest, shares outstanding (in shares)	128,702,000	128,333,000

The valuation allowance as of the balance sheet date to reduce the gross amount of receivables to estimated net realizable value, which would be presented in parentheses on the face of the balance sheet.

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Face amount or stated value per share of common stock.

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