Note 10 - Stock-based Compensation - Stock Incentive Plans Activity, Restricted Stock (Details) - Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Balance, Shares (in shares) | shares	411,074
Balance, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 59.13
Granted, Shares (in shares) | shares	144,152
Granted, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 82.90
Vested, Shares (in shares) | shares	(240,433)
Vested, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 47.45
Forfeited, Shares (in shares) | shares	(15,809)
Forfeited, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 79.34
Balance, Shares (in shares) | shares	298,984
Balance, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 80.37