Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets
Loans held-for-sale	$ 107,417	$ 221,784
Derivative assets	177,810	263,349
Liabilities
Derivative liabilities	23,683	19,256
Interest rate contracts
Assets
Derivative assets	164,438	248,267
Liabilities
Derivative liabilities	21,945	14,681
Risk participation agreements
Assets
Derivative assets	27	62
Liabilities
Derivative liabilities	63	125
Forward foreign exchange contracts
Assets
Derivative assets	623	0
Liabilities
Derivative liabilities	1,375	617
Interest rate lock commitments
Assets
Derivative assets	6,907	14,561
Liabilities
Derivative liabilities	0	0
Forward loan sales commitments
Assets
Derivative assets	5,515	0
Liabilities
Derivative liabilities	0	3,374
Power Equity CDs
Assets
Derivative assets	300	459
Liabilities
Derivative liabilities	300	459
Recurring
Assets
Investment securities available-for-sale	8,403,788	8,284,723
Loans held-for-sale	107,417	221,784
Interest-only strips	6,737	7,823
Derivative assets	178,591	263,401
Assets held in trust for deferred compensation plans	49,669	48,659
Total assets at fair value	8,746,202	8,826,390
Liabilities
Derivative liabilities	24,310	21,132
Liabilities held in trust for deferred compensation plans	49,669	48,659
Total liabilities at fair value	73,979	69,791
Recurring \| Interest rate contracts
Assets
Derivative assets	164,438	248,267
Liabilities
Derivative liabilities	21,945	14,681
Recurring \| Risk participation agreements
Assets
Derivative assets	27	62
Liabilities
Derivative liabilities	63	125
Recurring \| Forward foreign exchange contracts
Assets
Derivative assets	1,193	11
Liabilities
Derivative liabilities	1,505	2,386
Recurring \| Interest rate lock commitments
Assets
Derivative assets	7,073	14,565
Liabilities
Derivative liabilities	166	4
Recurring \| Forward loan sales commitments
Assets
Derivative assets	5,560	37
Liabilities
Derivative liabilities	45	3,411
Recurring \| Power Equity CDs
Assets
Derivative assets	300	459
Liabilities
Derivative liabilities	300	459
Recurring \| Swap agreement
Liabilities
Derivative liabilities	286	66
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
Assets held in trust for deferred compensation plans	49,669	48,659
Total assets at fair value	49,669	48,659
Liabilities
Derivative liabilities	0	0
Liabilities held in trust for deferred compensation plans	49,669	48,659
Total liabilities at fair value	49,669	48,659
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	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	8,403,321	8,284,219
Loans held-for-sale	107,417	221,784
Interest-only strips	0	0
Derivative assets	178,591	263,401
Assets held in trust for deferred compensation plans	0	0
Total assets at fair value	8,689,329	8,769,404
Liabilities
Derivative liabilities	24,024	21,066
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	24,024	21,066
Recurring \| Level 2 \| Interest rate contracts
Assets
Derivative assets	164,438	248,267
Liabilities
Derivative liabilities	21,945	14,681
Recurring \| Level 2 \| Risk participation agreements
Assets
Derivative assets	27	62
Liabilities
Derivative liabilities	63	125
Recurring \| Level 2 \| Forward foreign exchange contracts
Assets
Derivative assets	1,193	11
Liabilities
Derivative liabilities	1,505	2,386
Recurring \| Level 2 \| Interest rate lock commitments
Assets
Derivative assets	7,073	14,565
Liabilities
Derivative liabilities	166	4
Recurring \| Level 2 \| Forward loan sales commitments
Assets
Derivative assets	5,560	37
Liabilities
Derivative liabilities	45	3,411
Recurring \| Level 2 \| Power Equity CDs
Assets
Derivative assets	300	459
Liabilities
Derivative liabilities	300	459
Recurring \| Level 2 \| Swap agreement
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3
Assets
Investment securities available-for-sale	467	504
Loans held-for-sale	0	0
Interest-only strips	6,737	7,823
Derivative assets	0	0
Assets held in trust for deferred compensation plans	0	0
Total assets at fair value	7,204	8,327
Liabilities
Derivative liabilities	286	66
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	286	66
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	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	$ 66

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