Securities - Schedule of Available-for-Sales Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,359,102	$ 1,363,902
Gross Unrealized Gains	2,714	898
Gross Unrealized Losses	18,206	32,142
Fair Value	1,343,610	1,332,658
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	280	289
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	280	289
Obligations of U.S. Government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	478,819	493,371
Gross Unrealized Gains	360	80
Gross Unrealized Losses	3,434	7,553
Fair Value	475,745	485,898
Obligations of U.S. states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	87,459	86,260
Gross Unrealized Gains	488	113
Gross Unrealized Losses	169	933
Fair Value	87,778	85,440
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	147,971	131,831
Gross Unrealized Gains	684	168
Gross Unrealized Losses	2,645	3,732
Fair Value	146,010	128,267
U.S. Government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	642,054	649,620
Gross Unrealized Gains	1,182	537
Gross Unrealized Losses	11,908	19,599
Fair Value	631,328	630,558
Non-U.S. Government agencies or sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19	31
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	19	31
U.S. corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,500	2,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	50	325
Fair Value	$ 2,450	$ 2,175