Borrowings - Summary of Repurchase Agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Securities Sold Under Agreements to Repurchase
Repurchase agreements	$ 1,004,583	$ 569,824
Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase agreements	1,004,583	569,824
State and local governments | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase agreements	787,016	0
Corporate bonds | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase agreements	217,567	0
Residential mortgage-backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase agreements	0	312,015
Commercial mortgage-backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase agreements	$ 0	$ 257,809