Summary of Significant Accounting Policies - Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure Summary Of Significant Accounting Policies Accumulated Other Comprehensive Income [Abstract]
Beginning Balance, Gross		$ 0	$ 10,222	$ 137,555
Contract settlements reclassified to income, Gross			(10,222)	(120,443)
Change in unrealized deferred hedging gains (losses), Gross				(6,890)
Ending Balance, Gross			0	10,222
Beginning Balance, Tax Effect		0	(3,986)	(53,646)
Contract settlements reclassified to income, Tax Effect			3,986	46,973
Change in unrealized deferred hedging (losses) gains, tax effect				2,687
Ending Balance, Tax Effect			0	(3,986)
Beginning Balance, Net of Tax		0	6,236	83,909
Contract settlements reclassified to income, Net of Tax			(6,236)	(73,470)
Change in unrealized deferred hedging (losses) gains, net of taxes	[1]	$ 0	0	(4,203)
Ending Balance, Net of Tax			$ 0	$ 6,236

[1] Amounts are net of income tax benefit of $2,687 for the year ended December 31, 2013.