Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 13,391	$ 15,345
Property and equipment, accumulated depreciation	$ 465,983	$ 446,977
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	170,040	171,582
Common stock, shares outstanding	170,040	171,582