CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accumulated amortization on deferred charges	$ 31,071	$ 27,848
Common shares, par value	$ 0.10	$ 0.10
Common shares, shares authorized	500,000,000	500,000,000
Common shares, shares issued	315,239,299	277,114,784
Treasury at cost	977,673	833,934