Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Allowance for uncollectible accounts	$ 5,154	$ 5,152
Shareholders' equity:
Common stock, par value
Common stock, shares authorized	240,000,000	240,000,000
Common stock, shares issued	105,939,000	105,763,000