Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Taxes computed at statutory rate, amount	$ 59,418	$ 84,766	$ 75,553
State income taxes, net of federal income tax benefit, amount	2,595	4,649	2,352
Tax-exempt interest, amount	(7,849)	(6,301)	(6,487)
Bank owned life insurance, amount	(3,798)	(3,554)	(3,926)
Tax credits, amount	(12,495)	(16,577)	(15,743)
Other, net, amount	433	3,482	761
Income tax expense	$ 38,304	$ 66,465	$ 52,510
Taxes computed at statutory rate	35.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit	2.00%	2.00%	1.00%
Tax-exempt interest	(5.00%)	(3.00%)	(3.00%)
Bank owned life insurance	(2.00%)	(1.00%)	(2.00%)
Tax credits	(7.00%)	(7.00%)	(7.00%)
Other, net		1.00%
Income tax expense	23.00%	27.00%	24.00%