Unaudited Selected Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Revenue, Net	$ 182,723	$ 197,265	$ 203,889	$ 213,643	$ 278,622	$ 276,135	$ 267,562	$ 262,903	$ 797,520	$ 1,085,222	$ 1,073,508
Cost of Services and Goods Sold	124,709	129,050	134,619	144,274	168,517	166,927	168,158	161,669
Other operating expenses	34,372	21,397	21,377	26,652	19,655	20,088	15,270	18,407
Income Before Interest Expense and Taxes	23,642	46,818	47,893	42,717	90,450	89,120	84,134	82,827	161,070	346,531	333,419
Interest Expense and (Gain) Loss on Extinguishment of Debt	3,390	3,471	3,116	2,403	2,882	2,561	2,794	2,363
Income before income tax expense	20,252	43,347	44,777	40,314	87,568	86,559	81,340	80,464	148,690	335,931	324,102
Income Tax Expense (Benefit)	4,658	9,753	10,075	9,272	20,841	19,909	17,244	19,311	33,758	77,305	80,908
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	15,594	33,594	34,702	31,042	66,727	66,650	64,096	61,153	114,932	258,626	243,194
Net Income (Loss) Attributable to Noncontrolling Interest	176	190	76	(357)	537	153	362	89	85	1,141	383
Net Income (Loss) Attributable to Parent	$ 15,418	$ 33,404	$ 34,626	$ 31,399	$ 66,190	$ 66,497	$ 63,734	$ 61,064	$ 114,847	$ 257,485	$ 242,811
Earnings Per Share, Basic	$ 0.36	$ 0.79	$ 0.81	$ 0.72	$ 1.51	$ 1.51	$ 1.43	$ 1.36	$ 2.69	$ 5.80	$ 5.31
Earnings Per Share, Diluted	$ 0.36	$ 0.78	$ 0.81	$ 0.72	$ 1.51	$ 1.50	$ 1.42	$ 1.35	$ 2.68	$ 5.77	$ 5.28
Weighted Average Number of Shares Outstanding, Basic	42,355	42,517	42,790	43,340	43,742	44,152	44,660	44,908	42,747	44,362	45,692
Weighted Average Number of Shares Outstanding, Diluted	42,518	42,685	42,959	43,466	43,927	44,381	44,910	45,182	42,908	44,600	45,994