Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRS - Credit Quality Indicators by Class (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Accruing TDRs		$ 1,441	$ 1,866
Special Mention and Substandard Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Accruing TDRs		236,000	630
Total corporate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		9,781,002	9,147,470
Total corporate loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		9,317,176	8,758,739
Total corporate loans | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	191,174	194,180
Total corporate loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	218,800	146,865
Total corporate loans | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	53,852	47,686
Commercial and industrial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		4,524,401	4,120,293
Accruing TDRs		236	246
Commercial and industrial | Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		4,326,163	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]	74,221	74,878
Commercial and industrial | Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	104,208	59,842
Commercial and industrial | Commercial and industrial | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	19,809	33,507
Commercial and industrial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		430,589	430,928
Accruing TDRs		0	0
Commercial and industrial | Agricultural | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		383,404	407,542
Commercial and industrial | Agricultural | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	23,834	10,070
Commercial and industrial | Agricultural | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	16,639	11,752
Commercial and industrial | Agricultural | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	6,712	1,564
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		4,826,012	4,596,249
Accruing TDRs		343	738
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		4,607,609	4,399,131
Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	93,119	109,232
Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	97,953	75,271
Commercial real estate | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	27,331	12,615
Commercial real estate | Office, retail, and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		1,936,577	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		1,833,410	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]	41,134	35,853
Commercial real estate | Office, retail, and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	44,158	43,128
Commercial real estate | Office, retail, and industrial | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	17,875	6,510
Commercial real estate | Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		787,155	764,185
Accruing TDRs		167	557
Commercial real estate | Multi-family | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		765,375	745,131
Commercial real estate | Multi-family | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	10,385	9,273
Commercial real estate | Multi-family | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	6,073	6,674
Commercial real estate | Multi-family | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	5,322	3,107
Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		654,607	649,337
Accruing TDRs		0	0
Commercial real estate | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		632,922	624,446
Commercial real estate | Construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[1],[2]	12,591	16,370
Commercial real estate | Construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	8,942	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		1,447,673	1,361,810
Accruing TDRs		176	181
Commercial real estate | Other commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class		1,375,902	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]	29,009	47,736
Commercial real estate | Other commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[2],[3]	38,780	17,092
Commercial real estate | Other commercial real estate | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
Credit Quality Indicators by Class	[4]	$ 3,982	$ 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 $236,000 as of June 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.