Securities - Fair Values and Amortized Costs Securities (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost		$ 690,251
Debt Securities, Gross Unrealized Gains		3,070	$ 5,645
Debt Securities, Gross Unrealized Losses		(10,867)	(3,967)
Debt Securities, Fair Value		682,454	693,147
Equity Securities, Fair Value		5,196	5,144
Total Securities, Amortized Cost			695,284
Total Securities, Gross Unrealized Gains			6,975
Total Securities, Gross Unrealized Losses			(3,968)
Total Securities, Fair Value		687,650	698,291
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost		14,951	19,943
Debt Securities, Gross Unrealized Gains		0	0
Debt Securities, Gross Unrealized Losses		(290)	(154)
Debt Securities, Fair Value		14,661	19,789
Obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost		161,844	162,045
Debt Securities, Gross Unrealized Gains		62	341
Debt Securities, Gross Unrealized Losses		(1,317)	(193)
Debt Securities, Fair Value		160,589	162,193
Collateralized mortgage obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost		105,063	109,916
Debt Securities, Gross Unrealized Gains		2	93
Debt Securities, Gross Unrealized Losses		(2,483)	(1,321)
Debt Securities, Fair Value		102,582	108,688
Residential mortgage-backed securities of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost		30,700	32,388
Debt Securities, Gross Unrealized Gains		443	679
Debt Securities, Gross Unrealized Losses		(460)	(213)
Debt Securities, Fair Value		30,683	32,854
Commercial mortgage-backed securities of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost		255,043	244,018	[1]
Debt Securities, Gross Unrealized Gains		0	247	[1]
Debt Securities, Gross Unrealized Losses		(6,245)	(2,044)	[1]
Debt Securities, Fair Value		248,798	242,221	[1]
Securities purchased pending settlement			5,900
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost		122,650	123,159
Debt Securities, Gross Unrealized Gains		2,563	4,285
Debt Securities, Gross Unrealized Losses		(72)	(42)
Debt Securities, Fair Value		125,141	127,402
Total Debt Securities Available-for-Sale
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Amortized Cost		690,251	691,469
Debt Securities, Gross Unrealized Gains		3,070	5,645
Debt Securities, Gross Unrealized Losses		(10,867)	(3,967)
Debt Securities, Fair Value		682,454	693,147
Total equity securities
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, FV-NI, Cost	[2]	0	3,815
Equity Securities, FV-NI, Unrealized Gain	[2]	0	1,330
Equity Securities, FV-NI, Unrealized Loss	[2]	0	(1)
Equity Securities, Fair Value	[2]	$ 0	$ 5,144

[1] Includes a $5.9 million security purchase that was pending settlement as of December 31, 2017.

[2] ASU 2016-01 was adopted January 1, 2018, resulting in separate classification of our marketable equity securities previously included in available-for-sale securities