Fair Value Measurements - Schedule of Level 3 Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	$ 641,382	$ 460,797
Held-to-maturity Securities, Fair Value	73,458	79,639
Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	3,089
Level 3 | Securities available for sale, at fair value | Recurring basis
Level 3 Financial Instruments Measured at Fair Value
Beginning balance	3,089	3,077
Total gains:
Included in other comprehensive income	4	12
Purchases, sales, issuances and settlements
Transfer in and/or out of Level 3		(3,093)	$ 0
Ending balance	0	3,089	3,077
Change in unrealized gains relating to assets still held at the reporting date	0	12
Level 3 | State tax credits held for sale, at fair value | Recurring basis
Level 3 Financial Instruments Measured at Fair Value
Beginning balance	3,585	5,941
Total gains:
Total gains:	101	177
Purchases, sales, issuances and settlements
Sales	(3,286)	(2,533)
Ending balance	400	3,585	$ 5,941
Change in unrealized gains relating to assets still held at the reporting date	885	(575)
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
Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	641,382	457,708
Total Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	641,382	460,797
Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	641,382	460,797
Obligations of U.S. Government-sponsored enterprises
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	99,224	107,660
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	99,224	107,660
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	99,224	107,660
Obligations of states and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	34,642	36,631
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	3,089
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	34,642	33,542
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	34,642	36,631
Residential mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	507,516	316,506
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	507,516	316,506
Residential mortgage-backed securities | Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	$ 507,516	$ 316,506