General - Schedule of Changes in Accounting Principles (Details) - USD ($) $ in Thousands	Jun. 30, 2021		Mar. 31, 2021	Jan. 01, 2021	Dec. 31, 2020		Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Assets:
Held to maturity securities	$ 1,721,414				$ 1,227,668
Loans	9,121,250				9,243,174
Allowance for credit losses - Loans	(199,775)	[1]	$ (201,082)		(130,648)	[1]	$ (121,119)	$ (99,454)	$ (80,284)
Net loans	8,921,475				9,112,526
Tax asset, deferred and receivable	36,924				12,340
Liabilities:
Allowance for credit losses on unfunded loan commitments	20,500		$ 20,500		0
Stockholder's Equity:
Retained Earnings	795,666				788,578
Impact of CECL Adoption
Assets:
Held to maturity securities				$ (245)
Loans				4,776
Allowance for credit losses - Loans				(74,055)	(74,055)
Net loans				(69,279)
Tax asset, deferred and receivable				21,984
Liabilities:
Allowance for credit losses on unfunded loan commitments	$ 20,500			20,500
Stockholder's Equity:
Retained Earnings				(68,040)
January 1, 2021 Post-CECL Adoption
Assets:
Held to maturity securities				1,227,423
Loans				9,247,950
Allowance for credit losses - Loans				(204,703)	$ (204,703)
Net loans				9,043,247
Tax asset, deferred and receivable				34,324
Liabilities:
Allowance for credit losses on unfunded loan commitments				20,500
Stockholder's Equity:
Retained Earnings				$ 720,538

[1] Beginning January 1, 2021, the amount is based on the current expected credit loss methodology. Prior to January 1, 2021, the amount is based on the incurred loss methodology. See additional details in NOTE 1. GENERAL of these Notes to Consolidated Condensed Financial Statement.