Investment Securities - Amortized cost and fair value for available for sale securities - (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment securities available for sale
Amortized Cost	$ 1,657,624	$ 1,002,166
Gross Unrealized Gains	5,903	5,847
Gross Unrealized Losses	(12,817)	(8,608)
Fair Value	1,650,710	999,405
Government-sponsored entities debt
Investment securities available for sale
Amortized Cost	86,535	85,488
Gross Unrealized Gains	51
Gross Unrealized Losses	(1,077)	(846)
Fair Value	85,509	84,642
State and municipal obligations
Investment securities available for sale
Amortized Cost	216,812	105,303
Gross Unrealized Gains	3,749	2,289
Gross Unrealized Losses	(124)	(190)
Fair Value	220,437	107,402
Mortgage-backed securities. issued by Government sponsored entities
Investment securities available for sale
Amortized Cost	1,350,200	807,717
Gross Unrealized Gains	2,103	3,085
Gross Unrealized Losses	(11,616)	(7,225)
Fair Value	1,340,687	803,577
Common Stock
Investment securities available for sale
Amortized Cost	4,077	3,658
Gross Unrealized Gains		473
Gross Unrealized Losses		(347)
Fair Value	$ 4,077	$ 3,784

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
-Subparagraph (b)
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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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