Note 8 - Income Taxes (Details Textual) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 2,400,000		$ 2,400,000		$ 2,400,000
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0		0		0
Unrecognized Tax Benefits, Interest on Income Taxes Expense			145,000		$ 145,000
Income Tax Expense (Benefit)	15,551,000	$ 9,423,000	35,714,000	$ 17,962,000
Accounting Standards Update 2016-09 [Member]
Income Tax Expense (Benefit)	$ (1,900,000)		$ (3,900,000)
Domestic Tax Authority [Member] | Latest Tax Year [Member]
Open Tax Year			2016
Domestic Tax Authority [Member] | Earliest Tax Year [Member]
Open Tax Year			2013
State and Local Jurisdiction [Member] | Latest Tax Year [Member]
Open Tax Year			2016
State and Local Jurisdiction [Member] | Earliest Tax Year [Member]
Open Tax Year			2012