Note 14 - Unaudited Quarterly Data (in thousands, except per share data) (Detail) - Quarterly Financial Data (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
Statements of Income Data:
Revenues	$ 211,079	$ 204,388	$ 197,481	$ 198,533	$ 185,885	$ 179,356	$ 168,392	$ 167,999	$ 811,481	$ 701,632	$ 620,385
Gross profit	47,318	41,203	45,713	45,642	42,596	39,959	37,708	38,274	179,876	158,537	144,311
Administrative, salary and payroll taxes	32,074	25,414	28,702	27,914	27,619	26,313	22,999	21,893	48,485	41,776	36,133
Net income	$ 11,835	$ 12,626	$ 14,071	$ 14,570	$ 12,310	$ 11,772	$ 13,224	$ 13,629	$ 53,102	$ 50,935	$ 44,323
Basic earnings per share (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 earnings per share (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
Gross profit	22.40%	20.20%	23.10%	23.00%	22.90%	22.30%	22.40%	22.80%
Administrative, salary and payroll taxes	15.20%	12.40%	14.50%	14.10%	14.90%	14.70%	13.70%	13.00%
Net income	5.60%	6.20%	7.10%	7.30%	6.60%	6.60%	7.90%	8.10%