Note 14 - Selected Interim Financial Data (Unaudited) - Summary of Quarterly Financial Information 1 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues	$ 27,881	$ 27,948	$ 27,300	$ 26,868	$ 27,323	$ 26,008	$ 25,358	$ 25,263	$ 109,997	$ 103,952	$ 93,005
Income from operations	8,503	9,109	8,316	6,530	7,474	7,356	7,320	7,354
Net income (loss)	$ (1,566)	$ 1,251	$ 308	$ (8,994)	$ (1,523)	$ (1,569)	$ (1,611)	$ (1,298)
Net income (loss) attributable to common stockholders (in dollars per share)	$ (632)	$ 505	$ 124	$ (3,630)	$ (615)	$ (631)	$ (650)	$ (469)
Basic and diluted net income (loss) per share (in dollars per share)	$ (0.04)	$ 0.02	$ 0	$ (0.21)	$ (0.04)	$ (0.04)	$ (0.04)	$ (0.03)