Income Taxes (Income Tax Computed by Applying U.S. Federal Statutory Income Tax Rate) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense computed at the statutory rate	$ 104,888	$ 106,823	$ 142,927
Effect of tax-exempt interest	(49,166)	(49,700)	(81,034)
Tax benefit on dividends paid in our 401k plan	(1,743)	(1,551)	(2,372)
Bank owned life insurance income	(774)	(710)	(1,116)
Non-deductible compensation	1,708	210	158
Non-deductible FDIC premiums	1,267	1,771	0
Non-deductible meals and entertainment	1,299	1,193	983
Net tax benefit from stock-based compensation	(2,447)	(3,865)	(9,062)
Deferred tax adjustment related to reduction in U.S. federal statutory income tax rate	0	(231)	(4,047)
Correction for prior year tax-exempt interest	0	0	(2,906)
Other	838	(177)	683
Income tax expense, as reported	$ 55,870	$ 53,763	$ 44,214