Income Taxes (Provision for Income Taxes) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Current Federal Tax Expense (Benefit)	$ 31,338	$ 49,582	$ 168,164
Current State and Local Tax Expense (Benefit)	2,843	3,103	12,112
Current Foreign Tax Expense (Benefit)	529	2,455	0
Current Income Tax Expense (Benefit)	34,710	55,140	180,276
Deferred Federal Income Tax Expense (Benefit)	36,911	(8,476)	16,910
Deferred State and Local Income Tax Expense (Benefit)	2,591	147	157
Deferred Foreign Income Tax Expense (Benefit)	(386)	(1,100)	0
Deferred Income Tax Expense (Benefit)	39,116	(9,429)	17,067
Income Tax Expense (Benefit)	$ 73,826	$ 45,711	$ 197,343