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Investment Securities - Summary of Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($)
$ in Thousands
Jun. 30, 2021
Dec. 31, 2020
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 2,908,746 $ 2,344,174
Gross Unrealized Holding Gain, Available-for-sale 39,509 55,099
Gross Unrealized Holding Loss, Available-for-sale (16,234) (350)
Investment securities available-for-sale $ 2,932,021 $ 2,398,923
Total Percent, Available-for-sale 100.00% 100.00%
Amortized Cost, Held-to-maturity $ 1,036,924 $ 578,626
Gross Unrealized Holding Gain, Held-to-maturity 23,794 25,703
Gross Unrealized Holding Loss, Held-to-maturity (5,195) (106)
Fair Value, Held-to-maturity $ 1,055,523 $ 604,223
Total Percent, Held-to-maturity 100.00% 100.00%
CMO/REMIC [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 660,322 $ 457,548
Gross Unrealized Holding Gain, Available-for-sale 3,575 5,515
Gross Unrealized Holding Loss, Available-for-sale (5,348) (249)
Investment securities available-for-sale $ 658,549 $ 462,814
Total Percent, Available-for-sale 22.46% 19.29%
Amortized Cost, Held-to-maturity $ 106,699 $ 145,309
Gross Unrealized Holding Gain, Held-to-maturity 2,298 5,202
Gross Unrealized Holding Loss, Held-to-maturity 0 0
Fair Value, Held-to-maturity $ 108,997 $ 150,511
Total Percent, Held-to-maturity 10.29% 25.11%
Government Agency/GSE [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Held-to-maturity $ 592,611 $ 98,663
Gross Unrealized Holding Gain, Held-to-maturity 10,233 5,877
Gross Unrealized Holding Loss, Held-to-maturity (4,115) 0
Fair Value, Held-to-maturity $ 598,729 $ 104,540
Total Percent, Held-to-maturity 57.15% 17.05%
Mortgage-backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 2,218,714 $ 1,857,030
Gross Unrealized Holding Gain, Available-for-sale 34,675 48,006
Gross Unrealized Holding Loss, Available-for-sale (10,886) (101)
Investment securities available-for-sale $ 2,242,503 $ 1,904,935
Total Percent, Available-for-sale 76.48% 79.41%
Amortized Cost, Held-to-maturity $ 124,894 $ 146,382
Gross Unrealized Holding Gain, Held-to-maturity 5,809 7,644
Gross Unrealized Holding Loss, Held-to-maturity (165) (32)
Fair Value, Held-to-maturity $ 130,538 $ 153,994
Total Percent, Held-to-maturity 12.05% 25.30%
Municipal Bonds [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 28,700 $ 28,707
Gross Unrealized Holding Gain, Available-for-sale 1,259 1,578
Gross Unrealized Holding Loss, Available-for-sale 0 0
Investment securities available-for-sale $ 29,959 $ 30,285
Total Percent, Available-for-sale 1.02% 1.26%
Amortized Cost, Held-to-maturity $ 212,720 $ 188,272
Gross Unrealized Holding Gain, Held-to-maturity 5,454 6,980
Gross Unrealized Holding Loss, Held-to-maturity (915) (74)
Fair Value, Held-to-maturity $ 217,259 $ 195,178
Total Percent, Held-to-maturity 20.51% 32.54%
Other Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 1,010 $ 889
Gross Unrealized Holding Gain, Available-for-sale 0 0
Gross Unrealized Holding Loss, Available-for-sale 0 0
Investment securities available-for-sale $ 1,010 $ 889
Total Percent, Available-for-sale 0.04% 0.04%