Fair Values Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets
Loans held-for-sale	$ 114,831	$ 18,070
Derivative assets	135,242	8,268
Liabilities
Derivative liabilities	9,779	3,365
Interest rate contracts
Assets
Derivative assets	130,079	7,514
Liabilities
Derivative liabilities	8,811	3,337
Forward foreign exchange contracts
Assets
Derivative assets	0	102
Liabilities
Derivative liabilities	159	0
Interest rate lock commitments
Assets
Derivative assets	4,546	652
Liabilities
Derivative liabilities	105	28
Forward loan sales commitments
Assets
Derivative assets	0
Liabilities
Derivative liabilities	87
Power Equity CDs
Assets
Derivative assets	617
Liabilities
Derivative liabilities	617
Recurring
Assets
Investment securities carried at fair value	5,579,835	2,470,065
Loans held-for-sale	114,831	18,070
Interest-only strips	14,078	16,835
Derivative assets	137,394	15,250
Forward loan sales commitments	404	152
Assets held in trust for deferred compensation plans	40,784	33,217
Total assets at fair value	5,887,326	2,553,589
Liabilities
Derivative liabilities	103,564	4,356
Forward loan sales commitments	284	178
Liabilities held in trust for deferred compensation plans	40,784	33,217
Total liabilities at fair value	144,632	37,751
Recurring \| Interest rate contracts
Assets
Derivative assets	130,391	7,909
Liabilities
Derivative liabilities	101,910	3,732
Recurring \| Forward foreign exchange contracts
Assets
Derivative assets	1,666	6,689
Liabilities
Derivative liabilities	315	13
Recurring \| Interest rate lock commitments
Assets
Derivative assets	4,554	652
Liabilities
Derivative liabilities	113	28
Recurring \| Forward loan sales commitments
Assets
Derivative assets	166
Liabilities
Derivative liabilities	253
Recurring \| Power Equity CDs
Assets
Derivative assets	617
Liabilities
Derivative liabilities	617
Recurring \| Swap agreement
Liabilities
Derivative liabilities	356	583
Recurring \| Level 1
Assets
Investment securities carried at fair value	0	0
Loans 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	40,784	33,217
Total assets at fair value	40,784	33,217
Liabilities
Derivative liabilities	0	0
Forward loan sales commitments	0	0
Liabilities held in trust for deferred compensation plans	40,784	33,217
Total liabilities at fair value	40,784	33,217
Recurring \| Level 1 \| Interest rate contracts
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
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 carried at fair value	5,579,407	2,470,061
Loans held-for-sale	114,831	0
Interest-only strips	0	0
Derivative assets	137,394	14,598
Forward loan sales commitments	404	0
Assets held in trust for deferred compensation plans	0	0
Total assets at fair value	5,832,036	2,484,659
Liabilities
Derivative liabilities	103,208	3,745
Forward loan sales commitments	284	0
Liabilities held in trust for deferred compensation plans	0	0
Total liabilities at fair value	103,492	3,745
Recurring \| Level 2 \| Interest rate contracts
Assets
Derivative assets	130,391	7,909
Liabilities
Derivative liabilities	101,910	3,732
Recurring \| Level 2 \| Forward foreign exchange contracts
Assets
Derivative assets	1,666	6,689
Liabilities
Derivative liabilities	315	13
Recurring \| Level 2 \| Interest rate lock commitments
Assets
Derivative assets	4,554	0
Liabilities
Derivative liabilities	113	0
Recurring \| Level 2 \| Forward loan sales commitments
Assets
Derivative assets	166
Liabilities
Derivative liabilities	253
Recurring \| Level 2 \| Power Equity CDs
Assets
Derivative assets	617
Liabilities
Derivative liabilities	617
Recurring \| Level 2 \| Swap agreement
Liabilities
Derivative liabilities	0	0
Recurring \| Level 3
Assets
Investment securities carried at fair value	428	4
Loans held-for-sale	0	18,070
Interest-only strips	14,078	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	14,506	35,713
Liabilities
Derivative liabilities	356	611
Forward loan sales commitments	0	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 \| 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	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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