Nature of Operations and Summary of Significant Accounting Policies - Schedule of CECL Adoption Impacts (Details) - USD ($) $ in Thousands		Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Assets:
Held to maturity securities		$ 2,179,802		$ 1,227,668
Loans		9,241,861		9,243,174
Allowance for credit losses - loans	[1]	(195,397)		(130,648)
Net loans		9,046,464		9,112,526
Tax asset, deferred and receivable		35,641		12,340
Liabilities:
Allowance for credit losses on unfunded loan commitments		20,500	$ 20,500	0
Stockholder's Equity:
Retained earnings		864,839		788,578
Impact of adopting ASC 326
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)
Balances, January 1, 2021 Post-ASC 326 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. NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES of these Notes to Consolidated Financial Statements.