Debt Securities - Credit Quality Indictors for HTM Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	$ 1,128,299	$ 189,836
Investment Grade | Moody's: Aaa | S&P: AAA
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	274,791	39,022
Investment Grade | Moody's: Aa1, Aa2, Aa3 | S&P: AA+, AA, AA-
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	812,759	123,664
Investment Grade | Moody's: A1, A2, A3 | S&P: A+, A, A-
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	38,739	27,150
Investment Grade | Moody’s: Baa1, Baa2, Baa3 | S&P's, BBB+, BBB, BBB-
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	0	0
Investment Grade | Moody's: Not Rated | S&P: Not Rated
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	2,010	0
Below investment grade
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Debt securities, held-to-maturity	$ 0	$ 0