Condensed Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
Statement of Financial Position [Abstract]
Allowance for uncollectible accounts receivable	$ 4,972	$ 4,866	$ 3,714	$ 3,385	$ 3,125
Preferred stock, shares authorized (in shares)	900,000	900,000	900,000	900,000	900,000
Convertible preferred stock, shares issued (in shares)	445,063	445,063	445,063	445,063	445,063
Convertible preferred stock, shares outstanding (in shares)	445,063	445,063	445,063	445,063	445,063
Convertible preferred stock, liquidation preference	$ 20,444	$ 20,111	$ 20,111	$ 19,777	$ 19,777
Preferred stock, par value (in dollars per share)	$ 0	$ 0	$ 0	$ 0	$ 0
Preferred stock, shares authorized (in shares)	1,800,000	1,800,000	1,800,000	1,800,000	1,800,000
Preferred stock, shares issued (in shares)	0	0	0	0	0
Common stock, par value (in dollars per share)	$ 0	$ 0	$ 0	$ 0	$ 0
Common stock, shares authorized (in shares)	640,000,000	640,000,000	640,000,000	640,000,000	640,000,000
Common stock, shares issued (in shares)	60,008,481	60,008,481	60,019,438	60,013,718	60,012,155
Common stock, shares outstanding (in shares)	60,008,481	60,008,481	60,019,438	60,013,718	60,012,155