Investment Securities - Expected Maturities of Investment Securities Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 28, 2018
Investments Debt And Equity Securities [Abstract]
Available-for-Sale, Maturity, Within one year, Amortized Cost	$ 155,063
Available-for-Sale, Maturity, One to five years, Amortized Cost	2,900,031
Available-for-Sale, Maturity, Five to ten years, Amortized Cost	767,785
Available-for-Sale, Maturity, Beyond ten years, Amortized Cost	1,011,706
Available-for-Sale, Amortized Cost	4,834,585	$ 4,172,617
Held-to-Maturity, Maturity, Within one year, Amortized Cost	3,621
Held-to-Maturity, Maturity, One to five years, Amortized Cost	108,113
Held-to-Maturity, Maturity, Five to ten years, Amortized Cost	106,591
Held-to-Maturity, Maturity, Beyond ten years, Amortized Cost	188,956
Held-to-Maturity, Amortized Cost	407,281	506,334	$ 512,207
Available-for-Sale, Maturity, Within one year, Fair Value	154,941
Available-for-Sale, Maturity, One to five years, Fair Value	2,941,365
Available-for-Sale, Maturity, Five to ten years, Fair Value	787,301
Available-for-Sale, Maturity, Beyond ten years, Fair Value	1,033,372
Available-for-Sale securities, Fair Value	4,916,979	4,123,416	$ 3,272,456
Held-to-Maturity, Maturity, Within one year, Fair Value	3,644
Held-to-Maturity, Maturity, One to five years, Fair Value	111,340
Held-to-Maturity, Maturity, Five to ten years, Fair Value	111,513
Held-to-Maturity, Maturity, Beyond ten years, Fair Value	199,091
Held-to-Maturity, Fair Value	$ 425,588	$ 506,103		$ 505,566
Available-for-Sale, Maturity, Within one year, Weighted Average Yield	2.47%
Available-for-Sale, Maturity, One to five years, Weighted Average Yield	2.78%
Available-for-Sale, Maturity, Five to ten years, Weighted Average Yield	3.17%
Available-for-Sale, Maturity, Beyond ten years, Weighted Average Yield	3.23%
Available-for-Sale, Weighted Average Yield	2.93%
Held-to-Maturity, Maturity, Within one year, Weighted Average Yield	3.66%
Held-to-Maturity, Maturity, One to five years, Weighted Average Yield	3.28%
Held-to-Maturity, Maturity, Five to ten years, Weighted Average Yield	3.96%
Held-to-Maturity, Maturity, Beyond ten years, Weighted Average Yield	4.22%
Held-to-Maturity, Weighted Average Yield	3.90%