Fair Values Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets
Loans held-for-sale	$ 458,553	$ 91,202
Derivative assets	316,103	106,102
Liabilities
Derivative liabilities	20,978	9,203
Interest rate contracts
Assets
Derivative assets	296,955	102,401
Liabilities
Derivative liabilities	14,061	5,549
Risk participation agreements
Assets
Derivative assets	88	202
Liabilities
Derivative liabilities	123	354
Forward foreign exchange contracts
Assets
Derivative assets	1	0
Liabilities
Derivative liabilities	1,709	2,305
Interest rate lock commitments
Assets
Derivative assets	18,524	2,765
Liabilities
Derivative liabilities	0	13
Forward loan sales commitments
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	4,550	248
Power Equity CDs
Assets
Derivative assets	535	734
Liabilities
Derivative liabilities	535	734
Recurring
Assets
Investment securities available-for-sale	7,219,373	6,720,001
Loans held-for-sale	458,553	91,202
Interest-only strips	11,811	12,813
Derivative assets	320,937	106,642
Forward loan sales commitments, non-derivative		46
Assets held in trust for deferred compensation plans	43,203	43,743
Total assets at fair value	8,053,877	6,974,447
Liabilities
Derivative liabilities	23,562	14,312
Liabilities held in trust for deferred compensation plans	43,203	43,743
Total liabilities at fair value	66,765	58,055
Recurring \| Interest rate contracts
Assets
Derivative assets	299,207	102,893
Liabilities
Derivative liabilities	16,313	6,040
Recurring \| Risk participation agreements
Assets
Derivative assets	88	202
Liabilities
Derivative liabilities	123	354
Recurring \| Forward foreign exchange contracts
Assets
Derivative assets	2,519
Liabilities
Derivative liabilities	1,764	6,519
Recurring \| Interest rate lock commitments
Assets
Derivative assets	18,525	2,772
Liabilities
Derivative liabilities	1	20
Recurring \| Forward loan sales commitments
Assets
Derivative assets	63	41
Liabilities
Derivative liabilities	4,613	289
Recurring \| Power Equity CDs
Assets
Derivative assets	535	734
Liabilities
Derivative liabilities	535	734
Recurring \| Swap agreement
Liabilities
Derivative liabilities	213	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	43,203	43,743
Total assets at fair value	43,203	43,743
Liabilities
Derivative liabilities	0	0
Liabilities held in trust for deferred compensation plans	43,203	43,743
Total liabilities at fair value	43,203	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	7,218,932	6,719,568
Loans held-for-sale	458,553	91,202
Interest-only strips	0	0
Derivative assets	320,937	106,642
Forward loan sales commitments, non-derivative		46
Assets held in trust for deferred compensation plans	0	0
Total assets at fair value	7,998,422	6,917,458
Liabilities
Derivative liabilities	23,349	13,956
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	23,349	13,956
Recurring \| Level 2 \| Interest rate contracts
Assets
Derivative assets	299,207	102,893
Liabilities
Derivative liabilities	16,313	6,040
Recurring \| Level 2 \| Risk participation agreements
Assets
Derivative assets	88	202
Liabilities
Derivative liabilities	123	354
Recurring \| Level 2 \| Forward foreign exchange contracts
Assets
Derivative assets	2,519
Liabilities
Derivative liabilities	1,764	6,519
Recurring \| Level 2 \| Interest rate lock commitments
Assets
Derivative assets	18,525	2,772
Liabilities
Derivative liabilities	1	20
Recurring \| Level 2 \| Forward loan sales commitments
Assets
Derivative assets	63	41
Liabilities
Derivative liabilities	4,613	289
Recurring \| Level 2 \| Power Equity CDs
Assets
Derivative assets	535	734
Liabilities
Derivative liabilities	535	734
Recurring \| Level 2 \| Swap agreement
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3
Assets
Investment securities available-for-sale	441	433
Loans held-for-sale	0	0
Interest-only strips	11,811	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	12,252	13,246
Liabilities
Derivative liabilities	213	356
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	213	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	$ 213	$ 356

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