Debt Securities - Credit Quality Indictors for HTM Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
HTM debt securities
Debt securities, held-to-maturity	$ 193,509	$ 224,611
State and local governments
HTM debt securities
Debt securities, held-to-maturity	193,509	224,611
State and local governments | Moody's: Aaa | S&P: AAA | Investment Grade
HTM debt securities
Debt securities, held-to-maturity	40,735	65,217
State and local governments | Moody's: Aa1, Aa2, Aa3 | S&P: AA+, AA, AA- | Investment Grade
HTM debt securities
Debt securities, held-to-maturity	125,573	130,316
State and local governments | Moody's: A1, A2, A3 | S&P: A+, A, A- | Investment Grade
HTM debt securities
Debt securities, held-to-maturity	27,201	28,689
State and local governments | Moody's: Not Rated | S&P: Not Rated | Investment Grade
HTM debt securities
Debt securities, held-to-maturity	$ 0	$ 389