CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 2,307	$ 2,312
Long-term debt, debt discount and issuance costs	$ 5,574	$ 5,795
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, authorized	1,000,000	1,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	400,000,000	400,000,000
Common stock, issued	267,353,108	267,315,526
Common stock, outstanding	208,243,640	213,614,430
Treasury stock, shares	59,109,468	53,701,096