Investment Securities - Temporarily Impaired Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Fair Value (Estimated) (Less than 12 months)	$ 280,229	$ 148,611	$ 234,959
Unrealized Losses (Less than 12 months)	(7,761)	(2,100)	(4,910)
Fair Value (Estimated) (12 months or more)	132,575	144,394	7,652
Unrealized Losses (12 months or more)	(6,993)	(3,843)	(200)
Fair Value (Estimated)	412,804	293,005	242,611
Unrealized Losses	(14,754)	(5,943)	(5,110)
U.S. Government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Fair Value (Estimated) (Less than 12 months)	6,882	7,161	7,972
Unrealized Losses (Less than 12 months)	(373)	(94)	(181)
Fair Value (Estimated) (12 months or more)	3,689	3,814	0
Unrealized Losses (12 months or more)	(211)	(86)	0
Fair Value (Estimated)	10,571	10,975	7,972
Unrealized Losses	(584)	(180)	(181)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value (Estimated) (Less than 12 months)	202,673	132,025	170,966
Unrealized Losses (Less than 12 months)	(5,660)	(1,857)	(2,613)
Fair Value (Estimated) (12 months or more)	91,977	101,707	7,643
Unrealized Losses (12 months or more)	(3,757)	(2,693)	(197)
Fair Value (Estimated)	294,650	233,732	178,609
Unrealized Losses	(9,417)	(4,550)	(2,810)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value (Estimated) (Less than 12 months)	70,674	9,425	55,952
Unrealized Losses (Less than 12 months)	(1,728)	(149)	(2,115)
Fair Value (Estimated) (12 months or more)	36,909	38,864	0
Unrealized Losses (12 months or more)	(3,025)	(1,061)	0
Fair Value (Estimated)	107,583	48,289	55,952
Unrealized Losses	$ (4,753)	(1,210)	(2,115)
Other equity securities
Debt Securities, Available-for-sale [Line Items]
Fair Value (Estimated) (Less than 12 months)		0	69
Unrealized Losses (Less than 12 months)		0	(1)
Fair Value (Estimated) (12 months or more)		9	9
Unrealized Losses (12 months or more)		(3)	(3)
Fair Value (Estimated)		9	78
Unrealized Losses		$ (3)	$ (4)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
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