Fair Values Measurements - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held-for-sale	$ 91,202	$ 18,070
Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	6,720,001	2,470,065
Loans and leases held-for-sale	91,202	18,070
Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	0	0
Loans and leases held-for-sale	0	0
Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	6,719,568	2,470,061
Loans and leases held-for-sale	91,202	0
Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	433	4
Loans and leases held-for-sale	0	18,070
Carrying Amount | Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held-for-sale	108,584	72,594
Net loans	31,699,285	16,398,860
Securitization receivable	19,689	19,432
Deferred fees on commitments to extend credit	19,300	18,555
Total financial instrument assets	32,428,743	16,749,947
Certificates of deposits	7,455,556	4,790,680
Long-term borrowings	2,354,448	1,449,472
Deferred fees on standby letters of credit	56	77
Total financial instrument liabilities	9,810,060	6,240,229
Carrying Amount | Recurring | FHLB and FRB stocks
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	442,440	91,654
Carrying Amount | Recurring | Investment securities held-to-maturity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	139,445	148,852
Estimated Fair Value | Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held-for-sale	112,525	74,078
Net loans	31,804,513	16,399,551
Securitization receivable	19,466	19,025
Deferred fees on commitments to extend credit	19,300	18,555
Total financial instrument assets	32,543,088	16,752,130
Certificates of deposits	7,460,577	4,820,442
Long-term borrowings	2,368,469	1,451,550
Deferred fees on standby letters of credit	56	77
Total financial instrument liabilities	9,829,102	6,272,069
Estimated Fair Value | Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held-for-sale	0	0
Net loans	0	0
Securitization receivable	0	0
Deferred fees on commitments to extend credit	0	0
Total financial instrument assets	0	0
Certificates of deposits	0	0
Long-term borrowings	0	0
Deferred fees on standby letters of credit	0	0
Total financial instrument liabilities	0	0
Estimated Fair Value | Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held-for-sale	110,252	0
Net loans	0	0
Securitization receivable	0	0
Deferred fees on commitments to extend credit	19,300	18,555
Total financial instrument assets	713,160	256,676
Certificates of deposits	7,460,577	4,820,442
Long-term borrowings	2,368,469	1,451,550
Deferred fees on standby letters of credit	56	77
Total financial instrument liabilities	9,829,102	6,272,069
Estimated Fair Value | Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held-for-sale	2,273	74,078
Net loans	31,804,513	16,399,551
Securitization receivable	19,466	19,025
Deferred fees on commitments to extend credit	0	0
Total financial instrument assets	31,829,928	16,495,454
Certificates of deposits	0	0
Long-term borrowings	0	0
Deferred fees on standby letters of credit	0	0
Total financial instrument liabilities	0	0
Estimated Fair Value | Recurring | FHLB and FRB stocks
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	442,440	91,654
Estimated Fair Value | Recurring | FHLB and FRB stocks | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	0	0
Estimated Fair Value | Recurring | FHLB and FRB stocks | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	442,440	91,654
Estimated Fair Value | Recurring | FHLB and FRB stocks | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	0	0
Estimated Fair Value | Recurring | Investment securities held-to-maturity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	144,844	149,267
Estimated Fair Value | Recurring | Investment securities held-to-maturity | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	0	0
Estimated Fair Value | Recurring | Investment securities held-to-maturity | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	141,168	146,467
Estimated Fair Value | Recurring | Investment securities held-to-maturity | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	$ 3,676	$ 2,800