CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Allowance for doubtful accounts	$ 0	$ 37,912,000
Property and equipment, accumulated depreciation	97,788,000	88,298,000
Intangible assets, accumulated amortization	$ 47,120,000	$ 40,436,000
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares, issued (in shares)	128,064,145	127,634,012
Common stock, shares, outstanding (in shares)	128,064,145	127,634,012
Treasury stock, at cost (in shares)	287,248	5,106
Series A Preferred Stock
Convertible preferred stock series, par value (in dollars per share)	$ 0.0001	$ 0.0001
Convertible preferred stock series, shares authorized (in shares)	825,000	825,000
Convertible preferred stock series, shares issued (in shares)	21,630	21,645
Convertible preferred stock series, shares outstanding (in shares)	21,630	21,645
Convertible preferred stock series, liquidation preference	$ 3,172,000	$ 2,916,000
Series C Preferred Stock
Convertible preferred stock series, par value (in dollars per share)	$ 0.0001	$ 0.0001
Convertible preferred stock series, shares authorized (in shares)	625,000	625,000
Convertible preferred stock series, shares issued (in shares)	614,177	614,177
Convertible preferred stock series, shares outstanding (in shares)	614,177	614,177
Convertible preferred stock series, liquidation preference	$ 92,038,000	$ 84,555,000