Note R - Selected Quarterly Financial Data (Unaudited) (Details) - Quarterly Financial Data (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Abstract]
Contract revenue	$ 276,426	$ 264,796	$ 263,860	$ 245,052	$ 229,759	$ 244,055	$ 241,568	$ 233,921	$ 1,050,134	$ 949,303	$ 937,133
Operating income	16,610	18,528	17,574	16,650	12,587	17,154	17,295	17,649	69,362	64,685	66,182
Net income	$ 8,763	$ 11,553	$ 9,998	$ 9,716	$ 7,756	$ 11,131	$ 10,331	$ 10,112	$ 40,030	$ 39,330	$ 38,075
Earnings per share:
Basic (in Dollars per share)	$ 0.45	$ 0.59	$ 0.51	$ 0.49	$ 0.39	$ 0.56	$ 0.52	$ 0.52	$ 2.04	$ 1.99	$ 1.94
Diluted (in Dollars per share)	$ 0.44	$ 0.59	$ 0.50	$ 0.48	$ 0.38	$ 0.55	$ 0.52	$ 0.51	$ 2.00	$ 1.95	$ 1.91
Weighted-average common shares outstanding
Basic (in Shares)	19,409	19,450	19,795	19,804	19,826	19,802	19,706	19,543
Diluted (in Shares)	19,744	19,713	20,082	20,277	20,233	20,165	19,996	19,875	19,997,000	20,186,000	19,957,000