Fair Value Measurements - Schedule of Level 3 Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	$ 1,135,317	$ 721,369
Debt Securities, Held-to-maturity, Fair Value	181,939	63,934
Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Other Investments		0
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Other Investments		121
Fair Value	0	0
Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Other Investments		0
Fair Value	1,135,317	721,369
Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Other Investments		121
Fair Value	1,135,317	721,369
Obligations of U.S. Government-sponsored enterprises
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	10,046	98,498
Obligations of U.S. Government-sponsored enterprises | Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Obligations of U.S. Government-sponsored enterprises | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Obligations of U.S. Government-sponsored enterprises | Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	10,046	98,498
Obligations of U.S. Government-sponsored enterprises | Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	10,046	98,498
Obligations of states and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	213,024	26,810
Debt Securities, Held-to-maturity, Fair Value	11,874	12,408
Obligations of states and political subdivisions | Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Obligations of states and political subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Obligations of states and political subdivisions | Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	213,024	26,810
Obligations of states and political subdivisions | Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	213,024	26,810
Residential mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	902,021	586,136
Debt Securities, Held-to-maturity, Fair Value	47,021	51,526
Residential mortgage-backed securities | Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Residential mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Residential mortgage-backed securities | Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	902,021	586,136
Residential mortgage-backed securities | Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	902,021	586,136
US Treasury Bill Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	10,226	9,925
US Treasury Bill Securities [Member] | Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value		0
US Treasury Bill Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
US Treasury Bill Securities [Member] | Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	10,226	9,925
US Treasury Bill Securities [Member] | Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	$ 10,226	$ 9,925