Securities - Amortized Cost and Fair Value of Securities, by Contractual Maturities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Securities [Line Items]
Available for Sale, Due in one year or less, Amortized Cost	$ 84,929
Available for Sale, Due from one to five years, Amortized Cost	330,096
Available for Sale, Due from five to ten years, Amortized Cost	21,064
Available for Sale, Due after ten years, Amortized Cost	7,282
Available for Sale, with contractual maturities, Amortized Cost	443,371
Total securities available for sale, Amortized Cost	2,260,021	$ 1,636,526	$ 1,534,771
Available for Sale, Due in one year or less, Fair Value	85,222
Available for Sale, Due from one to five years, Fair Value	327,428
Available for Sale, Due from five to ten years, Fair Value	20,973
Available for Sale, Due after ten years, Fair Value	6,764
Available for Sale, with contractual maturities, Fair Value	440,387
Total securities available for sale, Fair Value	2,231,987	1,630,567	1,534,065
Held to Maturity, Due in one year or less, Amortized Cost	10,395
Held to Maturity, Due from one to five years, Amortized Cost	271,662
Held to Maturity, Due from five to ten years, Amortized Cost	50,994
Held to Maturity, Due after ten years, Amortized Cost	357,442
Securities Held To Maturity, with contractual maturities, Amortized Cost	690,493
Held to Maturity, with contractual maturities, Amortized Cost	2,337,342	1,637,061	1,453,355
Held to Maturity, Due in one year or less, Fair Value	10,404
Held to Maturity, Due from one to five years, Fair Value	267,497
Held to Maturity, Due from five to ten years, Fair Value	50,567
Held to Maturity, Due after ten years, Fair Value	339,853
Securities Held To Maturity, with contractual maturities, Fair Value	668,321
Held to Maturity, with contractual maturities, Fair Value	2,294,777	1,643,416	1,468,258
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	1,267,535	703,069	546,572
Total securities available for sale, Fair Value	1,252,798
Held to Maturity, with contractual maturities, Amortized Cost	852,215	709,970	677,169
Held to Maturity, with contractual maturities, Fair Value	849,224	718,652	693,535
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	546,659	503,328	580,601
Total securities available for sale, Fair Value	535,974
Held to Maturity, with contractual maturities, Amortized Cost	743,148	499,694	501,965
Held to Maturity, with contractual maturities, Fair Value	725,794	492,840	496,494
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	891	1,177	1,414
Total securities available for sale, Fair Value	897
Held to Maturity, with contractual maturities, Amortized Cost	1,689	2,681	4,285
Held to Maturity, with contractual maturities, Fair Value	1,686	2,695	4,313
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	1,292	4,299	7,891
Total securities available for sale, Fair Value	1,291
Held to Maturity, with contractual maturities, Amortized Cost	49,797	51,258	17,560
Held to Maturity, with contractual maturities, Fair Value	49,752	51,114	17,739
Equity Securities [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	273	$ 975	$ 1,031
Total securities available for sale, Fair Value	$ 640