Investment Securities - Summary of Amortized Cost and Estimated Fair Value of Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized Cost	$ 2,375,637	$ 2,345,791
Securities available-for-sale, Gross Unrealized Gains	87,787	28,270
Securities available-for-sale, Gross Unrealized Losses	1,780	5,469
Securities available-for-sale, Estimated Fair Value	2,461,644	2,368,592
Obligations of U.S. Government Agencies
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized Cost	70,225	69,464
Securities available-for-sale, Gross Unrealized Gains	221	57
Securities available-for-sale, Gross Unrealized Losses	458	415
Securities available-for-sale, Estimated Fair Value	69,988	69,106
Residential Pass-through \| Guaranteed by GNMA
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized Cost	99,869	98,122
Securities available-for-sale, Gross Unrealized Gains	2,799	1,205
Securities available-for-sale, Gross Unrealized Losses		245
Securities available-for-sale, Estimated Fair Value	102,668	99,082
Residential Pass-through \| Issued by FNMA and FHLMC
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized Cost	1,453,735	1,423,771
Securities available-for-sale, Gross Unrealized Gains	52,507	13,128
Securities available-for-sale, Gross Unrealized Losses		1,402
Securities available-for-sale, Estimated Fair Value	1,506,242	1,435,497
Other Residential Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized Cost	268,906	292,019
Securities available-for-sale, Gross Unrealized Gains	11,249	4,197
Securities available-for-sale, Gross Unrealized Losses		384
Securities available-for-sale, Estimated Fair Value	280,155	295,832
Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized Cost	271,590	276,533
Securities available-for-sale, Gross Unrealized Gains	11,580	2,448
Securities available-for-sale, Gross Unrealized Losses	941	3,023
Securities available-for-sale, Estimated Fair Value	282,229	275,958
Total MBS
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized Cost	2,094,100	2,090,445
Securities available-for-sale, Gross Unrealized Gains	78,135	20,978
Securities available-for-sale, Gross Unrealized Losses	941	5,054
Securities available-for-sale, Estimated Fair Value	2,171,294	2,106,369
Obligations of States and Municipal Subdivisions
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized Cost	211,312	185,882
Securities available-for-sale, Gross Unrealized Gains	9,431	7,235
Securities available-for-sale, Gross Unrealized Losses	381
Securities available-for-sale, Estimated Fair Value	$ 220,362	$ 193,117

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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+ References

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