Quarterly Selected Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 549,480	$ 619,467	$ 570,222	$ 555,183	$ 650,963	$ 633,180	$ 592,349	$ 575,295	$ 2,294,352	$ 2,451,787	$ 2,324,623
Gross profit	23,144	93,681	88,032	86,794	101,396	109,740	77,663	81,198
Income from operations	(6,960)	106,481	66,570	76,779	86,490	82,886	44,595	65,167	242,870	279,138	234,336
Reorganization items, net	(47)	0	(16)	87	(60)	(560)	(740)	(301)	24	(1,661)	(2,398)
Net income	$ (8,551)	$ 106,769	$ 62,840	$ 72,741	$ 86,094	$ 123,192	$ 43,306	$ 59,985	$ 233,799	$ 312,577	$ 238,450
Diluted earnings per common share (in dollars per share)	$ (0.57)	$ 6.34	$ 3.53	$ 3.91	$ 4.44	$ 6.10	$ 2.06	$ 2.74	$ 13.52	$ 15.15	$ 9.84