Note 9 - Equity-based Compensation - Summary of Stock Appreciation Rights (Details) - Stock Appreciation Rights (SARs) [Member] - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Outstanding, stock appreciation rights (in shares)	136,000
Outstanding, weighted average exercise price (in dollars per share)	$ 426.80
Outstanding, Beginning Balance, weighted average fair value (in dollars per share)	88.07
Outstanding, Beginning Balance, weighted average fair value (in dollars per share)	$ 95.74	$ 88.07
Outstanding, aggregate intrinsic value	$ 36,118	$ 26,510
Weighted Average Remaining Contractual Term, Outstanding (Year)	8 years 146 days	8 years 255 days
Granted, stock appreciation rights (in shares)	21,572
Granted, weighted average exercise price (in dollars per share)	$ 620.64
Granted, weighted average fair value (in dollars per share)	$ 138.01
Weighted Average Remaining Contractual Term, Granted (Year)	9 years 182 days
Exercised, stock appreciation rights (in shares)	(6,775)
Exercised, weighted average exercise price (in dollars per share)	$ 422.31
Exercised, weighted average fair value (in dollars per share)	87.22
Outstanding, weighted average exercise price (in dollars per share)	$ 456.72	$ 426.80
Forfeited, stock appreciation rights (in shares)	(8,700)
Vested and exercisable, stock appreciation rights (in shares)	24,150
Forfeited, weighted average exercise price (in dollars per share)	$ 422.31
Forfeited, weighted average fair value (in dollars per share)	87.22
Vested and exercisable, weighted average exercise price (in dollars per share)	422.81
Vested and exercisable, weighted average fair value (in dollars per share)	$ 87.33
Vested and exercisable, aggregate intrinsic value	$ 6,957
Outstanding, stock appreciation rights (in shares)	142,097	136,000
Weighted Average Remaining Contractual Term, Vested and exercisable (Year)	8 years 73 days