Note 10 - Common Stock and Stock-based Compensation Plans (Details Textual) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Mar. 31, 2019		Sep. 30, 2018	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Outstanding Number	[2]	684,479	[1]		702,817
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Exercisable Number	[2],[3]	610,513
Non-employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Annual Vesting, Percentage				25.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				4 years
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Outstanding Number		628,547
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Exercisable Number		555,947
Stock Appreciation Rights (SARs) [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards Granted				400.00%
Percentage of Stock Appreciation Rights Units Subject to Grant				75.00%
The2011 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights Vesting Percentage, Year One				25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Remaining Vesting Period				3 years
Stock Options and SARs [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 108
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition		1 year 36 days
Restricted Stock Units (RSUs) [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 18,786
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition		1 year 255 days

[1] Due to the ceiling imposed on the SAR grants, the outstanding amount equals a maximum of 628,547 shares of the Company's common stock issuable upon exercise.

[2] The SAR units are convertible for a maximum number of shares of the Company's common stock equal to 75% of the SAR units subject to the grant.

[3] Due to the ceiling imposed on the SAR grants, the exercisable amount equals a maximum of 555,947 shares of the Company's common stock issuable upon exercise.