Quarterly Financial Data (Unaudited) (Details) (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
Selected quarterly financial data and earnings per share [Abstract]
Revenues	$ 876,476	$ 795,525	$ 831,474	$ 877,489	$ 847,609	$ 755,995	$ 777,538	$ 663,846	$ 3,380,964	$ 3,044,988	$ 2,083,781
Earnings from continuing operations	7,648	8,337	5,497	6,050	5,044	9,266	3,355	5,778	27,532	23,443	8,552
Earnings from continuing operations, Per Share (in dollars per share)	$ 1.81	$ 1.98	$ 1.31	$ 1.43	$ 1.19	$ 2.20	$ 0.79	$ 1.37	$ 6.53	$ 5.55	$ 2.03
Net earnings	7,567	8,263	5,386	6,575	4,733	9,026	3,589	5,583	27,791	22,931	8,631
Net Earnings, Per Share (in dollars per share)	$ 1.79	$ 1.96	$ 1.28	$ 1.56	$ 1.13	$ 2.14	$ 0.85	$ 1.32	$ 6.59	$ 5.44	$ 2.05
Dividends	$ 2,615	$ 0	$ 0	$ 0	$ 2,404	$ 0	$ 0	$ 0	$ 2,615	$ 2,404	$ 2,277
Dividends, Per share (in dollars per share)	$ 0.62	$ 0	$ 0	$ 0	$ 0.57	$ 0	$ 0	$ 0	$ 0.62	$ 0.57