Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - Credit Quality Indicators by Class, Excluding Covered Loans (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Accruing		$ 1,796	$ 2,291
Special mention and substandard loans
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Accruing		657	834
Commercial, industrial, and agricultural | Commercial and industrial
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		3,529,914	2,827,658
Accruing		264	281
Commercial, industrial, and agricultural | Commercial and industrial | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		3,388,133	2,638,833
Commercial, industrial, and agricultural | Commercial and industrial | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	70,863	92,340
Commercial, industrial, and agricultural | Commercial and industrial | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	30,338	66,547
Commercial, industrial, and agricultural | Commercial and industrial | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	40,580	29,938
Commercial, industrial, and agricultural | Agricultural
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		430,886	389,496
Accruing		0	0
Commercial, industrial, and agricultural | Agricultural | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		413,946	366,382
Commercial, industrial, and agricultural | Agricultural | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	10,989	17,039
Commercial, industrial, and agricultural | Agricultural | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	5,732	5,894
Commercial, industrial, and agricultural | Agricultural | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	219	181
Commercial real estate loans
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		4,553,618	3,627,087
Accruing		766	1,009
Commercial real estate loans | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		4,395,481	3,488,742
Commercial real estate loans | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	72,749	50,296
Commercial real estate loans | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	69,621	67,283
Commercial real estate loans | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	15,767	20,766
Commercial real estate loans | Office, retail, and industrial
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		1,979,820	1,581,967
Accruing		0	155
Commercial real estate loans | Office, retail, and industrial | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		1,903,737	1,491,170
Commercial real estate loans | Office, retail, and industrial | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	25,546	34,007
Commercial real estate loans | Office, retail, and industrial | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	38,977	39,513
Commercial real estate loans | Office, retail, and industrial | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	11,560	17,277
Commercial real estate loans | Multi-family
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		675,463	614,052
Accruing		574	586
Commercial real estate loans | Multi-family | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		665,496	607,342
Commercial real estate loans | Multi-family | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	7,395	4,370
Commercial real estate loans | Multi-family | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	2,195	2,029
Commercial real estate loans | Multi-family | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	377	311
Commercial real estate loans | Construction
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		539,820	451,540
Accruing		0	0
Commercial real estate loans | Construction | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		521,911	438,946
Commercial real estate loans | Construction | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	10,184	111
Commercial real estate loans | Construction | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	7,516	12,197
Commercial real estate loans | Construction | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	209	286
Commercial real estate loans | Other commercial real estate
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		1,358,515	979,528
Accruing		192	268
Commercial real estate loans | Other commercial real estate | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		1,304,337	951,284
Commercial real estate loans | Other commercial real estate | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	29,624	11,808
Commercial real estate loans | Other commercial real estate | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	20,933	13,544
Commercial real estate loans | Other commercial real estate | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	3,621	2,892
Total corporate loans
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		8,514,418	6,844,241
Accruing		1,030	1,290
Total corporate loans | Pass
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class		8,197,560	6,493,957
Total corporate loans | Special Mention
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[1],[2]	154,601	159,675
Total corporate loans | Substandard
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[2],[3]	105,691	139,724
Total corporate loans | Non-accrual
Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Details) - Credit Quality Indicators by Class, Excluding Covered Loans [Line Items
Credit Quality Indicators by Class	[4]	$ 56,566	$ 50,885

[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 $657,000 as of December 31, 2017 and $834,000 as of December 31, 2016.

[3] Loans categorized as substandard exhibit a well-defined weakness 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 a well-defined weakness that may jeopardize the liquidation of the debt or result in a loss if the deficiencies are not corrected.