Components of Current and Deferred Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current income tax expense (benefit):
Federal and foreign									$ 27,937	$ 27,290	$ 23,703
State and local									1,476	1,036	446
Subtotal									29,413	28,326	24,149
Deferred income tax expense (benefit):
Federal and foreign									7,004	16,881	4,658
State and local									0	0	0
Subtotal									7,004	16,881	4,658
Actual tax expense and rate	$ 6,072	$ 8,723	$ 9,195	$ 12,427	$ 8,823	$ 15,032	$ 7,998	$ 13,354	$ 36,417	$ 45,207	$ 28,807