Fair Values Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets
Loans held-for-sale	$ 206,366	$ 91,202
Derivative assets	294,856	106,102
Liabilities
Derivative liabilities	23,175	9,203
Interest rate contracts
Assets
Derivative assets	281,195	102,401
Liabilities
Derivative liabilities	13,755	5,549
Risk participation agreements
Assets
Derivative assets	22	202
Liabilities
Derivative liabilities	118	354
Forward foreign exchange contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	2,305
Interest rate lock commitments
Assets
Derivative assets	13,130	2,765
Liabilities
Derivative liabilities	0	13
Forward loan sales commitments
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	8,793	248
Power Equity CDs
Assets
Derivative assets	509	734
Liabilities
Derivative liabilities	509	734
Recurring
Assets
Investment securities available-for-sale	7,025,224	6,720,001
Loans held-for-sale	206,366	91,202
Interest-only strips	10,951	12,813
Derivative assets	306,289	106,642
Forward loan sales commitments, non-derivative		46
Assets held in trust for deferred compensation plans	42,493	43,743
Total assets at fair value	7,591,323	6,974,447
Liabilities
Derivative liabilities	27,906	14,312
Liabilities held in trust for deferred compensation plans	42,493	43,743
Total liabilities at fair value	70,399	58,055
Recurring \| Interest rate contracts
Assets
Derivative assets	283,410	102,893
Liabilities
Derivative liabilities	15,970	6,040
Recurring \| Risk participation agreements
Assets
Derivative assets	22	202
Liabilities
Derivative liabilities	118	354
Recurring \| Forward foreign exchange contracts
Assets
Derivative assets	9,188
Liabilities
Derivative liabilities	2,200	6,519
Recurring \| Interest rate lock commitments
Assets
Derivative assets	13,134	2,772
Liabilities
Derivative liabilities	4	20
Recurring \| Forward loan sales commitments
Assets
Derivative assets	26	41
Liabilities
Derivative liabilities	8,819	289
Recurring \| Power Equity CDs
Assets
Derivative assets	509	734
Liabilities
Derivative liabilities	509	734
Recurring \| Swap agreement
Liabilities
Derivative liabilities	286	356
Recurring \| Level 1
Assets
Investment securities available-for-sale	0	0
Loans held-for-sale	0	0
Interest-only strips	0	0
Derivative assets	0	0
Forward loan sales commitments, non-derivative		0
Assets held in trust for deferred compensation plans	42,493	43,743
Total assets at fair value	42,493	43,743
Liabilities
Derivative liabilities	0	0
Liabilities held in trust for deferred compensation plans	42,493	43,743
Total liabilities at fair value	42,493	43,743
Recurring \| Level 1 \| Interest rate contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 1 \| Risk participation agreements
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 1 \| Forward foreign exchange contracts
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 1 \| Interest rate lock commitments
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 1 \| Forward loan sales commitments
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 1 \| Power Equity CDs
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 1 \| Swap agreement
Liabilities
Derivative liabilities	0	0
Recurring \| Level 2
Assets
Investment securities available-for-sale	7,024,821	6,719,568
Loans held-for-sale	206,366	91,202
Interest-only strips	0	0
Derivative assets	306,289	106,642
Forward loan sales commitments, non-derivative		46
Assets held in trust for deferred compensation plans	0	0
Total assets at fair value	7,537,476	6,917,458
Liabilities
Derivative liabilities	27,620	13,956
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	27,620	13,956
Recurring \| Level 2 \| Interest rate contracts
Assets
Derivative assets	283,410	102,893
Liabilities
Derivative liabilities	15,970	6,040
Recurring \| Level 2 \| Risk participation agreements
Assets
Derivative assets	22	202
Liabilities
Derivative liabilities	118	354
Recurring \| Level 2 \| Forward foreign exchange contracts
Assets
Derivative assets	9,188
Liabilities
Derivative liabilities	2,200	6,519
Recurring \| Level 2 \| Interest rate lock commitments
Assets
Derivative assets	13,134	2,772
Liabilities
Derivative liabilities	4	20
Recurring \| Level 2 \| Forward loan sales commitments
Assets
Derivative assets	26	41
Liabilities
Derivative liabilities	8,819	289
Recurring \| Level 2 \| Power Equity CDs
Assets
Derivative assets	509	734
Liabilities
Derivative liabilities	509	734
Recurring \| Level 2 \| Swap agreement
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3
Assets
Investment securities available-for-sale	403	433
Loans held-for-sale	0	0
Interest-only strips	10,951	12,813
Derivative assets	0	0
Forward loan sales commitments, non-derivative		0
Assets held in trust for deferred compensation plans	0	0
Total assets at fair value	11,354	13,246
Liabilities
Derivative liabilities	286	356
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	286	356
Recurring \| Level 3 \| Interest rate contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3 \| Risk participation agreements
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3 \| Forward foreign exchange contracts
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3 \| Interest rate lock commitments
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3 \| Forward loan sales commitments
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3 \| Power Equity CDs
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3 \| Swap agreement
Liabilities
Derivative liabilities	$ 286	$ 356

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