Investment Securities - Investment Securities by External Credit Rating (Details) $ in Thousands	Mar. 31, 2022 USD ($)
Debt Securities, Available-for-sale [Line Items]
2022	$ 341,830
2021	1,621,739
2020	1,725,986
2019	328,743
2018	51,998
Prior	148,222
Total	4,218,518
Investment securities available-for-sale
Debt Securities, Available-for-sale [Line Items]
2022	341,830
2021	1,369,820
2020	1,002,372
2019	319,877
2018	48,474
Prior	139,722
Total	3,222,095
Investment securities available-for-sale | U.S. Treasury | Aaa - Aa3
Debt Securities, Available-for-sale [Line Items]
2022	0
2021	13,990
2020	0
2019	0
2018	0
Prior	0
Total	13,990
Investment securities available-for-sale | Agency | Aaa - Aa3
Debt Securities, Available-for-sale [Line Items]
2022	0
2021	22,827
2020	282,195
2019	23,967
2018	33,635
Prior	6,603
Total	369,227
Investment securities available-for-sale | Agency | Baa1 - Baa3
Debt Securities, Available-for-sale [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	0
Prior	6,550
Total	6,550
Investment securities available-for-sale | Corporate debt | Aaa - Aa3
Debt Securities, Available-for-sale [Line Items]
2022	39,946
2021	0
2020	0
2019	0
2018	0
Prior	0
Total	39,946
Investment securities available-for-sale | Corporate debt | Baa1 - Baa3
Debt Securities, Available-for-sale [Line Items]
2022	34,267
2021	52,711
2020	92,122
2019	25,664
2018	0
Prior	9,789
Total	214,553
Investment securities available-for-sale | Corporate debt | A1 - A3
Debt Securities, Available-for-sale [Line Items]
2022	74,565
2021	203,779
2020	62,222
2019	0
2018	0
Prior	0
Total	340,566
Investment securities available-for-sale | Municipal bonds | Aaa - Aa3
Debt Securities, Available-for-sale [Line Items]
2022	0
2021	43,333
2020	222,497
2019	136,748
2018	0
Prior	12,706
Total	415,284
Investment securities available-for-sale | Collateralized mortgage obligations | Aaa - Aa3
Debt Securities, Available-for-sale [Line Items]
2022	173,442
2021	260,990
2020	229,588
2019	74,720
2018	14,839
Prior	101,677
Total	855,256
Investment securities available-for-sale | Mortgage-backed securities | Aaa - Aa3
Debt Securities, Available-for-sale [Line Items]
2022	19,610
2021	772,190
2020	113,748
2019	58,778
2018	0
Prior	2,397
Total	966,723
Investment securities held-to-maturity
Debt Securities, Available-for-sale [Line Items]
2022	0
2021	251,919
2020	723,614
2019	8,866
2018	3,524
Prior	8,500
Total	996,423
Investment securities held-to-maturity | Municipal bonds | Aaa - Aa3
Debt Securities, Available-for-sale [Line Items]
2022	0
2021	116,523
2020	622,498
2019	8,866
2018	0
Prior	0
Total	747,887
Investment securities held-to-maturity | Mortgage-backed securities | Aaa - Aa3
Debt Securities, Available-for-sale [Line Items]
2022	0
2021	135,396
2020	101,116
2019	0
2018	2,942
Prior	7,596
Total	247,050
Investment securities held-to-maturity | Other | Baa1 - Baa3
Debt Securities, Available-for-sale [Line Items]
2022	0
2021	0
2020	0
2019	0
2018	582
Prior	904
Total	$ 1,486