CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accumulated amortization on deferred charges	$ 41,088	$ 38,796
Common shares, par value	$ 0.10	$ 0.10
Common shares, shares authorized	600,000,000	600,000,000
Common shares, shares issued	362,225,819	360,711,232
Treasury at cost	1,019,290	957,068
Class J Cumulative Redeemable Preferred Shares [Member]
Cumulative redeemable preferred shares, liquidation value	$ 500	$ 500
Cumulative redeemable preferred shares, shares authorized	750,000	750,000
Cumulative redeemable preferred shares, shares issued	400,000	400,000
Cumulative redeemable preferred shares, shares outstanding	400,000	400,000
Preferred stock dividend rate	6.50%	6.50%
Cumulative redeemable preferred shares, par value
Class K Cumulative Redeemable Preferred Shares [Member]
Cumulative redeemable preferred shares, liquidation value	$ 500	$ 500
Cumulative redeemable preferred shares, shares authorized	750,000	750,000
Cumulative redeemable preferred shares, shares issued	300,000	300,000
Cumulative redeemable preferred shares, shares outstanding	300,000	300,000
Preferred stock dividend rate	6.25%	6.25%
Cumulative redeemable preferred shares, par value