Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 15,300	$ 15,950
Common stock, par value per share (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	85,671,643	81,119,117
Common stock, shares outstanding (in shares)	85,278,859	80,722,258
Treasury stock, at cost (shares)	392,784	396,859