Components of Current and Deferred Income Tax Expense (Benefit) (Detail) - USD ($) $ 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
Current income tax expense (benefit):
Federal and foreign									$ 39,900	$ 27,937	$ 27,290
State and local									638	1,476	1,036
Subtotal									40,538	29,413	28,326
Deferred income tax expense (benefit):
Federal and foreign									(5,755)	7,004	16,881
State and local									0	0	0
Subtotal									(5,755)	7,004	16,881
Actual tax expense and rate	$ 9,866	$ 7,875	$ 7,053	$ 9,989	$ 6,072	$ 8,723	$ 9,195	$ 12,427	$ 34,783	$ 36,417	$ 45,207