Investment Securities - Amortized cost and fair value for available for sale securities - (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Investment securities available for sale
Amortized Cost	$ 1,317,027	$ 1,002,166	$ 909,150
Gross Unrealized Gains	9,505	5,847	16,663
Gross Unrealized Losses	(5,853)	(8,608)	(439)
Fair Value	1,320,679	999,405	925,374
Government-sponsored entities debt
Investment securities available for sale
Amortized Cost	86,521	85,488	62,996
Gross Unrealized Gains	72		20
Gross Unrealized Losses	(642)	(846)	(36)
Fair Value	85,951	84,642	62,980
State and municipal obligations
Investment securities available for sale
Amortized Cost	199,898	105,303	112,797
Gross Unrealized Gains	4,584	2,289	4,542
Gross Unrealized Losses	(188)	(190)	(15)
Fair Value	204,294	107,402	117,324
Mortgage-backed securities. issued by Government sponsored entities
Investment securities available for sale
Amortized Cost	1,027,827	807,717	729,699
Gross Unrealized Gains	4,673	3,085	11,721
Gross Unrealized Losses	(5,023)	(7,225)	(143)
Fair Value	1,027,477	803,577	741,277
Common Stock
Investment securities available for sale
Amortized Cost	2,781	3,658	3,658
Gross Unrealized Gains	176	473	380
Gross Unrealized Losses		(347)	(245)
Fair Value	2,957	3,784	3,793
Mortgage-backed securities issued by private label holdings
Investment securities available for sale
Fair Value	$ 0	$ 0	$ 0

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
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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