Business Segments (Long-Lived Assets) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 577,517	$ 572,123	$ 485,323	$ 430,045	$ 441,023	$ 442,443	$ 434,424	$ 406,851	$ 2,065,008	$ 1,724,741	$ 1,523,101
Long-Lived Assets	53,196				44,311				53,196	44,311
Domestic [Member]
Segment Reporting Information [Line Items]
Revenues									1,972,888	1,643,598	1,446,805
Long-Lived Assets	52,228				43,659				52,228	43,659
Foreign [Member]
Segment Reporting Information [Line Items]
Revenues									92,120	81,143	$ 76,296
Long-Lived Assets	$ 968				$ 652				$ 968	$ 652