Note 12 - Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Beginning Balance, Shares (in shares)			5,554,000
Beginning Balance, Weighted Average Exercise Price (in dollars per share)			$ 17.35
Granted, Shares (in shares)			1,010,000
Granted, Weighted Average Exercise Price (in dollars per share)			$ 19.58
Exercised, Shares (in shares)	(87,230)	(132,128)	(151,034)	(132,805)
Exercised, Weighted Average Exercise Price (in dollars per share)			$ 15.81
Forfeitures, Shares (in shares)			(26,000)
Forfeitures, Weighted Average Exercise Price (in dollars per share)			$ 16.43
Expired, Shares (in shares)			(27,000)
Expired, Weighted Average Exercise Price (in dollars per share)			$ 22.14
Ending Balance, Shares (in shares)	6,360,000		6,360,000
Ending Balance, Weighted Average Exercise Price (in dollars per share)	$ 17.78		$ 17.78
Ending Balance, Weighted Average Remaining Contractual Terms (Year)			5 years 135 days
Outstanding, Aggregate intrinsic value	$ 26,785		$ 26,785
Expected to Vest, Shares (in shares)	1,633,000		1,633,000
Expected to Vest, Weighted Average Exercise Price (in dollars per share)	$ 17.68		$ 17.68
Expected to Vest, Weighted Average Remaining Contractual Terms (Year)			8 years
Expected to Vest, Aggregate Intrinsic Value	$ 6,449		$ 6,449
Exercisable, Shares (in shares)	3,877,000		3,877,000
Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 17.87		$ 17.87
Exercisable, Weighted Average Remaining Contractual Terms (Year)			3 years 262 days
Exercisable, Aggregate Intrinsic Value	$ 16,929		$ 16,929