Note 9 - Employee Benefits (Detail) - Nonvested performance unit award activity: (Performance Shares [Member], USD $)	12 Months Ended
	Dec. 31, 2012
Performance Shares [Member]
Shares	60,166
Weighted Average Grant Date Fair Value (in Dollars per share)	$ 19.76
Granted	39,500
Granted (in Dollars per share)	$ 20.95
Vested	(23,120)	[1]
Vested (in Dollars per share)	$ 20.24
Shares	76,546
Weighted Average Grant Date Fair Value (in Dollars per share)	$ 20.23

[1] This number of performance unit award shares vested based on our financial performance in 2012 and was distributed or credited to the Marten Transport, Ltd. Deferred Compensation Plan in March 2013. The fair value of unit award shares that vested in 2012 was $468,000.