Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 9,247	$ 7,820
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, authorized	2,000	2,000
Preferred stock, issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	640,000	640,000
Common stock, issued	179,857	182,067
Common stock, outstanding	179,857	182,067