Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 10,504	$ 9,247
Property and equipment, accumulated depreciation	$ 405,043	$ 406,652
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	179,637	179,857
Common stock, shares outstanding	179,637	179,857