Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Trade accounts receivable, allowance for doubtful accounts	$ 11,729	$ 12,619
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares issued (in shares)	289,581,682	295,867,844
Common stock, shares outstanding (in shares)	289,581,682	295,867,844