Note 5 - Stock-Based Compensation (Detail) (USD $)	1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Maximum Period Of Common Stock Granted	10	10
Annual Increments To Be Vested In Common Stock Units	20.00%	20.00%
Stock or Unit Option Plan Expense		$ 129,000	$ 194,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in Shares)		0	39,784
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options			647,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value			34,000
(in Shares)	14,416			125,133	147,661
GrantSharesAveragePriceDuringPeriodRestrictedStockUnitAward (in Dollars per share)	$ 20.57			$ 18.24	$ 14.78
(in Shares)	14,416			125,133	147,661
(in Shares)	14,416			125,133	147,661
Restricted Stock Units (RSUs) [Member]
Stock or Unit Option Plan Expense		609,000	353,000
(in Shares)		14,416
(in Shares)		14,416
(in Shares)		14,416
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 2,400,000	$ 2,400,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition		1 year 6 months
2005 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in Shares)	2,674,892	2,674,892