Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for doubtful accounts	$ 4,634	$ 5,475
Preferred Stock, par value (in dollars per share)	$ 0	$ 0
Preferred Stock, Shares Authorized	50,000,000	50,000,000
Preferred Stock, Shares Outstanding	0	0
Common stock, par value (in dollars per share)	$ 0	$ 0
Voting Common Stock [Member]
Common Stock, Shares Authorized	400,000,000	400,000,000
Common Stock, Shares Issued	128,600,384	129,931,812
Common Stock, Shares Outstanding	128,600,384	129,931,812	87,695,495	47,802,816
Nonvoting Common Stock [Member]
Common Stock, Shares Authorized	400,000,000	400,000,000
Common Stock, Shares Outstanding	0	0	828,885