Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRS (Details) - Credit Quality Indicators by Class - USD ($)		Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Accruing		$ 2,112,000	$ 2,291,000
Special Mention and Substandard Loans
Financing Receivable, Recorded Investment [Line Items]
Accruing		674,000	834,000
Commercial loans
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		8,380,494,000	6,843,914,000
Commercial loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		7,948,402,000	6,493,630,000
Commercial loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	198,224,000	159,675,000
Commercial loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	187,347,000	139,724,000
Commercial loans | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	46,521,000	50,885,000
Commercial, industrial, and agricultural | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		3,370,780,000	2,827,658,000
Accruing		278,000	281,000
Commercial, industrial, and agricultural | Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		3,134,827,000	2,638,833,000
Commercial, industrial, and agricultural | Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	113,944,000	92,340,000
Commercial, industrial, and agricultural | Commercial and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	100,495,000	66,547,000
Commercial, industrial, and agricultural | Commercial and industrial | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	21,514,000	29,938,000
Commercial, industrial, and agricultural | Agricultural
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		422,784,000	389,496,000
Accruing		0	0
Commercial, industrial, and agricultural | Agricultural | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		405,354,000	366,382,000
Commercial, industrial, and agricultural | Agricultural | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	9,873,000	17,039,000
Commercial, industrial, and agricultural | Agricultural | Substandard
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	6,274,000	5,894,000
Commercial, industrial, and agricultural | Agricultural | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	1,283,000	181,000
Commercial real estate loans
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		4,586,930,000	3,626,760,000
Accruing		845,000	1,009,000
Commercial real estate loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		4,408,221,000	3,488,415,000
Commercial real estate loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	74,407,000	50,296,000
Commercial real estate loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	80,578,000	67,283,000
Commercial real estate loans | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	23,724,000	20,766,000
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		1,988,979,000	1,581,827,000
Accruing		0	155,000
Commercial real estate loans | Office, retail, and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		1,887,699,000	1,491,030,000
Commercial real estate loans | Office, retail, and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	39,545,000	34,007,000
Commercial real estate loans | Office, retail, and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	42,230,000	39,513,000
Commercial real estate loans | Office, retail, and industrial | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	19,505,000	17,277,000
Commercial real estate loans | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		671,710,000	614,034,000
Accruing		582,000	586,000
Commercial real estate loans | Multi-family | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		665,313,000	607,324,000
Commercial real estate loans | Multi-family | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	4,336,000	4,370,000
Commercial real estate loans | Multi-family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	1,898,000	2,029,000
Commercial real estate loans | Multi-family | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	163,000	311,000
Commercial real estate loans | Construction
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		568,460,000	451,540,000
Accruing		0	0
Commercial real estate loans | Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		542,862,000	438,946,000
Commercial real estate loans | Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	8,927,000	111,000
Commercial real estate loans | Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	16,473,000	12,197,000
Commercial real estate loans | Construction | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	198,000	286,000
Commercial real estate loans | Other commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		1,357,781,000	979,359,000
Accruing		263,000	268,000
Commercial real estate loans | Other commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class		1,312,347,000	951,115,000
Commercial real estate loans | Other commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[1],[2]	21,599,000	11,808,000
Commercial real estate loans | Other commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[2],[3]	19,977,000	13,544,000
Commercial real estate loans | Other commercial real estate | Non-Accrual
Financing Receivable, Recorded Investment [Line Items]
Credit Quality Indicators by Class	[4]	$ 3,858,000	$ 2,892,000

[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 $674,000 as of March 31, 2017 and $834,000 as of December 31, 2016.

[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.