Quarterly Financial Information (Unaudited) (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
Operating revenues	$ 1,016,099	$ 1,208,567	$ 1,043,948	$ 860,214	$ 1,016,826	$ 1,198,342	$ 938,039	$ 860,845	$ 4,128,828	$ 4,014,052	$ 4,115,073
Operating expenses	904,613	1,061,883	954,983	798,229	934,896	1,070,514	878,330	810,537	3,719,708	3,694,277	3,787,891
Operating income	111,486	146,684	88,965	61,985	81,930	127,828	59,709	50,308	409,120	319,775	327,182
Income from continuing operations	66,547	88,386	46,298	31,865	55,902	73,886	26,061	20,540	$ 233,096	$ 176,389	$ 185,027
Loss from discontinued operations attributable to the Company, net of tax	(816)	(5,400)	(155,451)	(6,996)	(3,368)	(213,334)	(255,665)	(326,457)
Net income (loss) attributable to parent	$ 65,731	$ 82,986	$ (109,153)	$ 24,869	$ 52,534	$ (139,448)	$ (229,604)	$ (305,917)
Earnings (loss) per common share - basic [Abstract]
Earnings before discontinued operations	$ 0.34	$ 0.45	$ 0.24	$ 0.16	$ 0.29	$ 0.38	$ 0.13	$ 0.10	$ 1.19	$ 0.90	$ 0.96
Discontinued operations attributable to the Company, net of tax	0.00	(0.03)	(0.80)	(0.03)	(0.02)	(1.10)	(1.31)	(1.67)	(0.86)	(4.10)	0.59
Earnings (loss) per common share - basic	$ 0.34	$ 0.42	$ (0.56)	$ 0.13	$ 0.27	$ (0.72)	$ (1.18)	$ (1.57)	$ 0.33	$ (3.20)	$ 1.55
Weighted average common shares outstanding - basic	195,304	195,304	195,304	195,284	195,266	195,151	194,805	194,479	195,299	194,928	192,507
Earnings per common share - diluted [Abstract]
Earnings before discontinued operations	$ 0.33	$ 0.45	$ 0.24	$ 0.16	$ 0.29	$ 0.38	$ 0.13	$ 0.10	$ 1.19	$ 0.90	$ 0.96
Discontinued operations attributable to the Company, net of tax	0.00	(0.03)	(0.80)	(0.03)	(0.02)	(1.10)	(1.31)	(1.67)	(0.86)	(4.10)	0.59
Earnings (loss) per common share - diluted	$ 0.33	$ 0.42	$ (0.56)	$ 0.13	$ 0.27	$ (0.72)	$ (1.18)	$ (1.57)	$ 0.33	$ (3.20)	$ 1.55
Weighted average common shares outstanding - diluted	195,889	195,811	195,699	195,284	195,324	195,169	194,838	194,566	195,618	194,986	192,587
Additional Information [Abstract]
Asset impairment charges						$ 14,100	$ 3,000
Withdrawal from multiemployer defined benefit plan [Member] | Operating Engineers Local 800 and WY Contractors Association Pension Plan for WY [Member]
Additional Information [Abstract]
Multiemployer plan withdrawal increase (decrease)	$ (11,100)							$ 2,400