Note 7 - Equity-Based Compensation (Detail) - Deferred Stock Unit Activity (Deferred Stock Units [Member], USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred Stock Units [Member]
Outstanding, beginning of period	173,916	163,318	147,374
Outstanding, beginning of period (in Dollars per share)	$ 20.12	$ 19.43	$ 18.22
Awarded	41,734	31,238	25,175
Awarded (in Dollars per share)	$ 17.78	$ 23.75	$ 26.10
Shares distributed	(34,132)	(20,640)	(9,231)
Shares distributed (in Dollars per share)	$ 22.90	$ 20.13	$ 18.38
Outstanding, end of period	181,518	173,916	163,318
Outstanding, end of period (in Dollars per share)	$ 19.06	$ 20.12	$ 19.43