Summary of Significant Accounting Policies New Accounting Pronouncements or Change in Accounting Principle (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on investment securities held-to-maturity	$ (312)		$ 0
Allowance for credit losses on loans and leases			(209,096)
Deferred Tax Assets, Tax Deferred Expense			61,975
Accrued expenses and other liabilities	266,374		153,161
Retained Earnings, Unappropriated			$ 2,061,352
Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on investment securities held-to-maturity	(397)	$ (397)
Allowance for credit losses on loans and leases	(57,568)	(266,664)		$ 0
Deferred Tax Assets, Tax Deferred Expense	15,891	77,866
Accrued expenses and other liabilities	9,139	162,300
Retained Earnings, Unappropriated	$ (51,213)	$ 2,010,139