Unaudited Selected Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue, Net	$ 149,542	$ 143,483	$ 148,069	$ 153,647	$ 182,723	$ 197,265	$ 203,889	$ 213,643	$ 594,741	$ 797,520	$ 1,085,222
Cost of Services and Goods Sold	112,678	107,153	109,999	112,814	124,709	129,050	134,619	144,274
Other operating expenses	15,340	14,842	17,843	17,893	34,372	21,397	21,377	26,652
Income Before Interest Expense and Taxes	21,524	21,488	20,227	22,940	23,642	46,818	47,893	42,717	86,179	161,070	346,531
Interest Expense and (Gain) Loss on Extinguishment of Debt	2,548	2,569	3,021	3,434	3,390	3,471	3,116	2,403
Income before income tax expense	18,976	18,919	17,206	19,506	20,252	43,347	44,777	40,314	74,607	148,690	335,931
Income Tax Expense (Benefit)	3,607	2,081	671	4,389	4,658	9,753	10,075	9,272	10,748	33,758	77,305
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	15,369	16,838	16,535	15,117	15,594	33,594	34,702	31,042	63,859	114,932	258,626
Net Income (Loss) Attributable to Noncontrolling Interest	(90)	108	(89)	35	176	190	76	(357)	(36)	85	1,141
Net Income (Loss) Attributable to Parent	$ 15,459	$ 16,730	$ 16,624	$ 15,082	$ 15,418	$ 33,404	$ 34,626	$ 31,399	$ 63,895	$ 114,847	$ 257,485
Earnings Per Share, Basic	$ 0.35	$ 0.38	$ 0.38	$ 0.36	$ 0.36	$ 0.79	$ 0.81	$ 0.72	$ 1.47	$ 2.69	$ 5.80
Earnings Per Share, Diluted	$ 0.35	$ 0.38	$ 0.38	$ 0.35	$ 0.36	$ 0.78	$ 0.81	$ 0.72	$ 1.46	$ 2.68	$ 5.77
Weighted Average Number of Shares Outstanding, Basic	44,113	44,110	43,297	42,380	42,355	42,517	42,790	43,340	43,479	42,747	44,362
Weighted Average Number of Shares Outstanding, Diluted	44,326	44,320	43,505	42,520	42,518	42,685	42,959	43,466	43,670	42,908	44,600