Note 5 - Recent Accounting Pronouncements (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent [Member]
Recognition and Measurement of Financial Instruments, Reclassification from AOCI to Retained Earnings, Tax Effect	$ 458,000
Retained Earnings [Member]
Recognition and Measurement of Financial Instruments, Reclassification from AOCI to Retained Earnings, Tax Effect	(458,000)
Accounting Standards Update 2016-01 [Member] | AOCI Attributable to Parent [Member]
Recognition and Measurement of Financial Instruments, Reclassification from AOCI to Retained Earnings, Tax Effect	458,000
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Recognition and Measurement of Financial Instruments, Reclassification from AOCI to Retained Earnings, Tax Effect	$ (458,000)
Accounting Standards Update 2016-09 [Member] | Additional Paid-in Capital [Member]
Current Period Reclassification Adjustment		$ (866,000)