Note 2 - Summary of Significant Accounting Policies (Detail) - Reconciliation between basic and diluted earnings per share (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income (in Dollars)	$ 11,835	$ 12,626	$ 14,071	$ 14,570	$ 12,310	$ 11,772	$ 13,224	$ 13,629	$ 53,102	$ 50,935	$ 44,323
Weighted average shares outstanding used in calculating basic earnings per share									14,878	15,013	14,832
Dilutive common share equivalents									174	204	237
Weighted average common and common equivalent shares used in calculating diluted earnings per share									15,052	15,217	15,069
Basic (in Dollars per share)	$ 0.81	$ 0.86	$ 0.93	$ 0.96	$ 0.82	$ 0.79	$ 0.88	$ 0.91	$ 3.57	$ 3.39	$ 2.99
Diluted (in Dollars per share)	$ 0.81	$ 0.85	$ 0.92	$ 0.95	$ 0.81	$ 0.77	$ 0.87	$ 0.90	$ 3.53	$ 3.35	$ 2.94
Options and restricted share units outstanding which are not included in the calculation of diluted earnings per share because their impact is anti-dilutive									34	77	108