Securities Available-for-Sale - Composition of Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 690,472	$ 686,205
Gross Unrealized Gains	9,925	10,754
Gross Unrealized Losses	(2,443)	(3,472)
Fair Value	697,954	693,487
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,930	24,891
Gross Unrealized Gains	2	47
Gross Unrealized Losses	(38)	(127)
Fair Value	24,894	24,811
Obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	195,194	230,989
Gross Unrealized Gains	1,171	1,573
Gross Unrealized Losses	(357)	(383)
Fair Value	196,008	232,179
Collateralized mortgage obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	115,027	130,046
Gross Unrealized Gains	476	465
Gross Unrealized Losses	(608)	(734)
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
Gross Unrealized Gains	896	984
Gross Unrealized Losses	(151)	(232)
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
Gross Unrealized Gains	511	243
Gross Unrealized Losses	(1,289)	(1,950)
Fair Value	192,604	125,604
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	123,672	128,783
Gross Unrealized Gains	5,632	3,772
Gross Unrealized Losses	0	(46)
Fair Value	129,304	132,509
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	686,657	678,626
Gross Unrealized Gains	8,688	7,084
Gross Unrealized Losses	(2,443)	(3,472)
Fair Value	692,902	682,238
Marketable equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,815	7,579
Gross Unrealized Gains	1,237	3,670
Gross Unrealized Losses	0	0
Fair Value	$ 5,052	$ 11,249

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Section 50
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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