Fair Values Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets
Loans and leases held-for-sale	$ 91,202	$ 18,070
Derivative assets	106,102	8,268
Liabilities
Derivative liabilities	9,203	3,365
Interest rate contracts
Assets
Derivative assets	102,401	7,489
Liabilities
Derivative liabilities	5,549	3,311
Risk participation agreements
Assets
Derivative assets	202	25
Liabilities
Derivative liabilities	354	26
Forward foreign exchange contracts
Assets
Derivative assets	0	102
Liabilities
Derivative liabilities	2,305	0
Interest rate lock commitments
Assets
Derivative assets	2,765	652
Liabilities
Derivative liabilities	13	28
Forward loan sales commitments
Assets
Derivative assets	0
Liabilities
Derivative liabilities	248
Power Equity CDs
Assets
Derivative assets	734
Liabilities
Derivative liabilities	734
Recurring
Assets
Investment securities available-for-sale	6,720,001	2,470,065
Loans and leases held-for-sale	91,202	18,070
Interest-only strips	12,813	16,835
Derivative assets	106,642	15,250
Forward loan sales commitments	46	152
Assets held in trust for deferred compensation plans	43,743	33,217
Total assets at fair value	6,974,447	2,553,589
Liabilities
Derivative liabilities	14,312	4,356
Forward loan sales commitments		178
Liabilities held in trust for deferred compensation plans	43,743	33,217
Total liabilities at fair value	58,055	37,751
Recurring \| Interest rate contracts
Assets
Derivative assets	102,893	7,884
Liabilities
Derivative liabilities	6,040	3,706
Recurring \| Risk participation agreements
Assets
Derivative assets	202	25
Liabilities
Derivative liabilities	354	26
Recurring \| Forward foreign exchange contracts
Assets
Derivative assets		6,689
Liabilities
Derivative liabilities	6,519	13
Recurring \| Interest rate lock commitments
Assets
Derivative assets	2,772	652
Liabilities
Derivative liabilities	20	28
Recurring \| Forward loan sales commitments
Assets
Derivative assets	41
Liabilities
Derivative liabilities	289
Recurring \| Power Equity CDs
Assets
Derivative assets	734
Liabilities
Derivative liabilities	734
Recurring \| Swap agreement
Liabilities
Derivative liabilities	356	583
Recurring \| Level 1
Assets
Investment securities available-for-sale	0	0
Loans and leases held-for-sale	0	0
Interest-only strips	0	0
Derivative assets	0	0
Forward loan sales commitments	0	0
Assets held in trust for deferred compensation plans	43,743	33,217
Total assets at fair value	43,743	33,217
Liabilities
Derivative liabilities	0	0
Forward loan sales commitments		0
Liabilities held in trust for deferred compensation plans	43,743	33,217
Total liabilities at fair value	43,743	33,217
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
Liabilities
Derivative liabilities	0
Recurring \| Level 1 \| Power Equity CDs
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Recurring \| Level 1 \| Swap agreement
Liabilities
Derivative liabilities	0	0
Recurring \| Level 2
Assets
Investment securities available-for-sale	6,719,568	2,470,061
Loans and leases held-for-sale	91,202	0
Interest-only strips	0	0
Derivative assets	106,642	14,598
Forward loan sales commitments	46	0
Assets held in trust for deferred compensation plans	0	0
Total assets at fair value	6,917,458	2,484,659
Liabilities
Derivative liabilities	13,956	3,745
Forward loan sales commitments		0
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	13,956	3,745
Recurring \| Level 2 \| Interest rate contracts
Assets
Derivative assets	102,893	7,884
Liabilities
Derivative liabilities	6,040	3,706
Recurring \| Level 2 \| Risk participation agreements
Assets
Derivative assets	202	25
Liabilities
Derivative liabilities	354	26
Recurring \| Level 2 \| Forward foreign exchange contracts
Assets
Derivative assets		6,689
Liabilities
Derivative liabilities	6,519	13
Recurring \| Level 2 \| Interest rate lock commitments
Assets
Derivative assets	2,772	0
Liabilities
Derivative liabilities	20	0
Recurring \| Level 2 \| Forward loan sales commitments
Assets
Derivative assets	41
Liabilities
Derivative liabilities	289
Recurring \| Level 2 \| Power Equity CDs
Assets
Derivative assets	734
Liabilities
Derivative liabilities	734
Recurring \| Level 2 \| Swap agreement
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3
Assets
Investment securities available-for-sale	433	4
Loans and leases held-for-sale	0	18,070
Interest-only strips	12,813	16,835
Derivative assets	0	652
Forward loan sales commitments	0	152
Assets held in trust for deferred compensation plans	0	0
Total assets at fair value	13,246	35,713
Liabilities
Derivative liabilities	356	611
Forward loan sales commitments		178
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	356	789
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	652
Liabilities
Derivative liabilities	0	28
Recurring \| Level 3 \| Forward loan sales commitments
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Recurring \| Level 3 \| Power Equity CDs
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Recurring \| Level 3 \| Swap agreement
Liabilities
Derivative liabilities	$ 356	$ 583

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