Quarterly Financial Data (Unaudited) (Narrative) (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
Effect of Fourth Quarter Events [Line Items]
Revenues	$ 66,492	$ 53,638	$ 21,047	$ 103,124	$ 178,058	$ 124,618	$ 138,066	$ 149,706	$ 244,301	$ 590,448	$ 581,225
Net Income (Loss) Attributable to Parent	$ (10,336)	$ 13,907	$ 4,148	$ 55,887	$ 100,574	$ 69,459	$ 78,264	$ 84,498	$ 63,606	$ 332,795	$ 322,244
Net income per basic share (in Dollars per Share)	$ (0.06)	$ 0.08	$ 0.03	$ 0.34	$ 0.61	$ 0.42	$ 0.48	$ 0.52	$ 0.39	$ 2.04	$ 2.04
Net income per diluted share (in Dollars per Share)	$ (0.06)	$ 0.08	$ 0.03	$ 0.34	$ 0.61	$ 0.42	$ 0.47	$ 0.50	$ 0.39	$ 2.03	$ 1.86