Fair Value Measurements - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	$ 460,172	$ 91,202
Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	7,446,163	6,720,001
Loans held-for-sale	460,172	91,202
Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	0	0
Loans held-for-sale	0	0
Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	7,445,696	6,719,568
Loans held-for-sale	460,172	91,202
Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	467	433
Loans held-for-sale	0	0
Carrying Amount | Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	255	108,584
Net loans and leases	31,140,162	31,699,285
Securitization receivable	0	19,689
Deferred fees on commitments to extend credit	21,222	19,300
Total financial instrument assets	31,632,392	32,428,743
Certificates of deposits	6,334,760	7,455,556
Long-term borrowings	871,845	2,354,448
Deferred fees on standby letters of credit		56
Total financial instrument liabilities	7,206,605	9,810,060
Carrying Amount | Recurring | FHLB and FRB stocks
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	300,444	442,440
Carrying Amount | Recurring | Investment securities held-to-maturity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	170,309	139,445
Estimated Fair Value | Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	262	112,525
Net loans and leases	31,323,032	31,804,513
Securitization receivable	19,802	19,466
Deferred fees on commitments to extend credit	21,222	19,300
Total financial instrument assets	31,845,126	32,543,088
Certificates of deposits	6,355,057	7,460,577
Long-term borrowings	901,221	2,368,469
Deferred fees on standby letters of credit		56
Total financial instrument liabilities	7,256,278	9,829,102
Estimated Fair Value | Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	0	0
Net loans and leases	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
Total financial instrument liabilities	0	0
Estimated Fair Value | Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	0	110,252
Net loans and leases	0	0
Securitization receivable	0	0
Deferred fees on commitments to extend credit	21,222	19,300
Total financial instrument assets	498,315	713,160
Certificates of deposits	6,355,057	7,460,577
Long-term borrowings	901,221	2,368,469
Deferred fees on standby letters of credit		56
Total financial instrument liabilities	7,256,278	9,829,102
Estimated Fair Value | Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	262	2,273
Net loans and leases	31,323,032	31,804,513
Securitization receivable	19,802	19,466
Deferred fees on commitments to extend credit	0	0
Total financial instrument assets	31,346,811	31,829,928
Certificates of deposits	0	0
Long-term borrowings	0	0
Deferred fees on standby letters of credit		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	300,444	442,440
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	300,444	442,440
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	180,364	144,844
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	176,649	141,168
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	$ 3,715	$ 3,676