Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Trade accounts receivable, allowance for doubtful accounts	$ 6,728	$ 5,647
Preferred stock, shares authorized	5,000,000	5,000,000
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	296,564,382	295,258,674
Common stock, shares outstanding	296,564,382	295,258,674