Note R - Selected Quarterly Financial Data (Unaudited) (Details) - Quarterly Financial Data (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Data [Abstract]
Contract revenue	$ 229,759	$ 244,055	$ 241,568	$ 233,921	$ 231,979	$ 237,864	$ 239,649	$ 227,641	$ 949,303	$ 937,133	$ 840,775
Operating income	12,587	17,154	17,295	17,649	14,545	16,995	18,268	16,374	64,685	66,182	59,481
Net income	$ 7,756	$ 11,131	$ 10,331	$ 10,112	$ 9,219	$ 9,573	$ 10,346	$ 8,937	$ 39,330	$ 38,075	$ 34,865
Earnings per share:
Basic (in Dollars per share)	$ 0.39	$ 0.56	$ 0.52	$ 0.52	$ 0.47	$ 0.49	$ 0.52	$ 0.45	$ 1.99	$ 1.94	$ 1.77
Diluted (in Dollars per share)	$ 0.38	$ 0.55	$ 0.52	$ 0.51	$ 0.47	$ 0.48	$ 0.52	$ 0.45	$ 1.95	$ 1.91	$ 1.75
Weighted-average common shares outstanding
Basic (in Shares)	19,826	19,802	19,706	19,543	19,501	19,610	19,774	19,769
Diluted (in Shares)	20,233	20,165	19,996	19,875	19,690	19,770	19,971	20,082	20,186	19,957	19,928