Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRS - Credit Quality Indicators by Class (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Accruing TDRs		$ 1,422	$ 1,866
Special Mention and Substandard Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Accruing TDRs		232,000	630
Total corporate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		9,760,970	9,147,470
Total corporate loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		9,336,861	8,758,739
Total corporate loans | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	185,369	194,180
Total corporate loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	171,963	146,865
Total corporate loans | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	66,777	47,686
Commercial and industrial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		4,570,361	4,120,293
Accruing TDRs		232	246
Commercial and industrial | Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		4,404,464	3,952,066
Commercial and industrial | Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	63,434	74,878
Commercial and industrial | Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	75,724	59,842
Commercial and industrial | Commercial and industrial | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	26,739	33,507
Commercial and industrial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		417,740	430,928
Accruing TDRs		0	0
Commercial and industrial | Agricultural | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		373,757	407,542
Commercial and industrial | Agricultural | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	22,495	10,070
Commercial and industrial | Agricultural | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	15,246	11,752
Commercial and industrial | Agricultural | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	6,242	1,564
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		4,772,869	4,596,249
Accruing TDRs		338	738
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		4,558,640	4,399,131
Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	99,440	109,232
Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	80,993	75,271
Commercial real estate | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	33,796	12,615
Commercial real estate | Office, retail, and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		1,892,877	1,820,917
Accruing TDRs		0	0
Commercial real estate | Office, retail, and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		1,793,811	1,735,426
Commercial real estate | Office, retail, and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	41,332	35,853
Commercial real estate | Office, retail, and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	30,922	43,128
Commercial real estate | Office, retail, and industrial | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	26,812	6,510
Commercial real estate | Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		817,444	764,185
Accruing TDRs		165	557
Commercial real estate | Multi-family | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		799,218	745,131
Commercial real estate | Multi-family | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	10,068	9,273
Commercial real estate | Multi-family | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	6,006	6,674
Commercial real estate | Multi-family | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	2,152	3,107
Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		637,256	649,337
Accruing TDRs		0	0
Commercial real estate | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		612,810	624,446
Commercial real estate | Construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	14,147	16,370
Commercial real estate | Construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	10,147	8,377
Commercial real estate | Construction | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	152	144
Commercial real estate | Other commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		1,425,292	1,361,810
Accruing TDRs		173	181
Commercial real estate | Other commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		1,352,801	1,294,128
Commercial real estate | Other commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	33,893	47,736
Commercial real estate | Other commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	33,918	17,092
Commercial real estate | Other commercial real estate | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	$ 4,680	$ 2,854

[1] Loans categorized as special mention exhibit potential weaknesses that require the close attention of management since these potential weaknesses may result in the deterioration of repayment prospects in the future.

[2] Total special mention and substandard loans includes accruing TDRs of $232,000 as of September 30, 2019 and $630,000 as of December 31, 2018.

[3] Loans categorized as substandard exhibit well-defined weaknesses that may jeopardize the liquidation of the debt. These loans continue to accrue interest because they are well-secured, and collection of principal and interest is expected within a reasonable time.

[4] Loans categorized as non-accrual exhibit well-defined weaknesses that may jeopardize the liquidation of the debt or result in a loss if the deficiencies are not corrected.