Investment Securities - Amortized cost and fair value for available for sale securities - (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Investment securities available for sale
Amortized cost	$ 1,614,571	$ 1,655,107	$ 1,336,379
Gross Unrealized Gains	2,042	5,903	10,477
Gross Unrealized Losses	(38,614)	(12,817)	(6,429)
Fair Value	1,577,999	1,648,193	1,340,427
Government-sponsored entities debt
Investment securities available for sale
Amortized cost	48,933	86,535	76,508
Gross Unrealized Gains		51	52
Gross Unrealized Losses	(1,320)	(1,077)	(608)
Fair Value	47,613	85,509	75,952
State and municipal obligations
Investment securities available for sale
Amortized cost	223,533	216,812	188,720
Gross Unrealized Gains	1,932	3,749	4,680
Gross Unrealized Losses	(1,649)	(124)	(106)
Fair Value	223,816	220,437	193,294
Mortgage-backed securities. issued by Government sponsored entities
Investment securities available for sale
Amortized cost	1,342,105	1,350,200	1,068,718
Gross Unrealized Gains	110	2,103	5,195
Gross Unrealized Losses	(35,645)	(11,616)	(5,316)
Fair Value	1,306,570	1,340,687	1,068,597
Corporate securities
Investment securities available for sale
Amortized cost		1,560	2,433
Gross Unrealized Gains			550
Gross Unrealized Losses			(399)
Fair Value		1,560	2,584
Mortgage-backed securities issued by private label holdings
Investment securities available for sale
Fair Value	$ 0	$ 0	$ 0

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

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- Definition

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

+ References

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- Definition

This item represents the cost of debt 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 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: 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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Amount of debt securities categorized neither as held-to-maturity nor trading.

+ References

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 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-Subparagraph (b)-(g)
-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803

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