Quarterly Financial Information (unaudited) (Detail) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Total operating revenues	$ 83,883	$ 54,479	$ 47,066	$ 49,606	$ 65,882	$ 71,172	$ 74,453	$ 43,814	$ 235,034	$ 255,321	$ 137,816
Total operating expenses	90,745	79,530	83,865	95,367	911,187	123,462	114,909	93,248	349,507	1,242,806	221,990
Operating loss	(6,862)	(25,051)	(36,799)	(45,761)	(845,305)	(52,290)	(40,456)	(49,434)	(114,473)	(987,485)	(84,174)
Net loss	$ (63,307)	$ (26,801)	$ (73,011)	$ (40,687)	$ (813,869)	$ (81,468)	$ (41,970)	$ (34,103)	$ (203,806)	$ (971,410)	$ (183,176)
Loss per share:
Basic and diluted	$ (0.23)	$ (0.10)	$ (0.33)	$ (0.18)	$ (3.66)	$ (0.37)	$ (0.19)	$ (0.17)	$ (0.84)	$ (4.46)	$ (1.27)