Fair Values Measurements - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	$ 206,366	$ 91,202
Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	7,025,224	6,720,001
Loans held-for-sale	206,366	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	7,024,821	6,719,568
Loans held-for-sale	206,366	91,202
Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available-for-sale	403	433
Loans held-for-sale	0	0
Carrying Amount | Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	80,811	108,584
Net loans and leases	32,833,843	31,699,285
Securitization receivable	19,753	19,689
Deferred fees on commitments to extend credit	20,078	19,300
Total financial instrument assets	33,574,565	32,428,743
Certificates of deposits	7,463,192	7,455,556
Long-term borrowings	2,600,594	2,354,448
Deferred fees on standby letters of credit	43	56
Total financial instrument liabilities	10,063,829	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	484,461	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	135,619	139,445
Estimated Fair Value | Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	83,635	112,525
Net loans and leases	33,154,484	31,804,513
Securitization receivable	19,577	19,466
Deferred fees on commitments to extend credit	20,078	19,300
Total financial instrument assets	33,908,209	32,543,088
Certificates of deposits	7,494,934	7,460,577
Long-term borrowings	2,583,975	2,368,469
Deferred fees on standby letters of credit	43	56
Total financial instrument liabilities	10,078,952	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	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	64,895	110,252
Net loans and leases	0	0
Securitization receivable	0	0
Deferred fees on commitments to extend credit	20,078	19,300
Total financial instrument assets	711,736	713,160
Certificates of deposits	7,494,934	7,460,577
Long-term borrowings	2,583,975	2,368,469
Deferred fees on standby letters of credit	43	56
Total financial instrument liabilities	10,078,952	9,829,102
Estimated Fair Value | Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-sale	18,740	2,273
Net loans and leases	33,154,484	31,804,513
Securitization receivable	19,577	19,466
Deferred fees on commitments to extend credit	0	0
Total financial instrument assets	33,196,473	31,829,928
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	484,461	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	484,461	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	145,974	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	142,302	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	$ 3,672	$ 3,676