Securities Available-for-Sale - Amortized Cost and Fair Value of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 690,472	$ 686,205
Fair Value	697,954	693,487
Obligations of the U.S. Treasury, U.S. government corporations and agencies, and obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	63,576
Due after one year through five years, Amortized Cost	177,864
Due after five years through ten years, Amortized Cost	56,875
Due after ten years, Amortized Cost	45,481
Available-for-sale Securities, Debt Maturities, Amortized Cost	343,796
Due in one year or less, Fair Value	63,646
Due after one year through five years, Fair Value	180,087
Due after five years through ten years, Fair Value	58,890
Due after ten years, Fair Value	47,583
Fair Value, Debt securities	350,206
Collateralized mortgage obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	115,027	130,046
Fair Value	114,895	129,777
Residential mortgage-backed securities of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,452	36,606
Fair Value	35,197	37,358
Commercial mortgage-backed securities of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	193,382	127,311
Fair Value	192,604	125,604
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	686,657	678,626
Fair Value	692,902	682,238
Marketable equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,815	7,579
Fair Value	$ 5,052	$ 11,249