Investment Securities - Amortized cost and fair value for available for sale securities - (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Investment securities available for sale
Amortized Cost	$ 1,378,658	$ 1,002,166	$ 962,067
Gross Unrealized Gains	9,927	5,847	16,493
Gross Unrealized Losses	(7,572)	(8,608)	(513)
Fair Value	1,381,013	999,405	978,047
Government-sponsored entities debt
Investment securities available for sale
Amortized Cost	93,995	85,488	126,360
Gross Unrealized Gains	25		96
Gross Unrealized Losses	(721)	(846)	(143)
Fair Value	93,299	84,642	126,313
State and municipal obligations
Investment securities available for sale
Amortized Cost	196,241	105,303	123,399
Gross Unrealized Gains	4,183	2,289	4,822
Gross Unrealized Losses	(140)	(190)	(78)
Fair Value	200,284	107,402	128,143
Mortgage-backed securities.
Investment securities available for sale
Amortized Cost	1,084,764	807,717	708,650
Gross Unrealized Gains	5,095	3,085	11,291
Gross Unrealized Losses	(6,420)	(7,225)	(111)
Fair Value	1,083,439	803,577	719,830
Common Stock
Investment securities available for sale
Amortized Cost	3,658	3,658	3,658
Gross Unrealized Gains	624	473	284
Gross Unrealized Losses	(291)	(347)	(181)
Fair Value	$ 3,991	$ 3,784	$ 3,761

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=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=66010992&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=73527792&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)
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