Investment securities (Unrealized Gain (Loss) on Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale
Amortized cost	$ 496,536	$ 307,648
Gross unrealized gains	2,847	4,108
Gross unrealized losses	(4,564)	(1,494)
Estimated fair value	494,819	310,262
Held-to-maturity
Amortized cost	140,557	139,424
Gross unrealized gains	1,965	2,843
Gross unrealized losses	(250)	(7)
Held-to-maturity	142,272	142,260
U.S. Agency mortgage-backed securities (MBS)
Available-for-sale
Amortized cost	165,933	154,691
Gross unrealized gains	1,828	2,698
Gross unrealized losses	(799)	(455)
Estimated fair value	166,962	156,934
Held-to-maturity
Amortized cost	101,563	98,800
Gross unrealized gains	1,195	1,875
Gross unrealized losses	(148)	(5)
Held-to-maturity	102,610	100,670
Non-agency MBS
Available-for-sale
Amortized cost	252,153	118,765
Gross unrealized gains	203	477
Gross unrealized losses	(3,408)	(1,016)
Estimated fair value	248,948	118,226
U.S. Agency asset-backed securities
Available-for-sale
Amortized cost	6,700	7,468
Gross unrealized gains	419	800
Gross unrealized losses	(57)	(23)
Estimated fair value	7,062	8,245
Corporate securities
Available-for-sale
Amortized cost	71,213	26,199
Gross unrealized gains	397	121
Gross unrealized losses	(287)	0
Estimated fair value	71,323	26,320
Mutual fund
Available-for-sale
Amortized cost	537	525
Gross unrealized gains	0	12
Gross unrealized losses	(13)	0
Estimated fair value	524	537
Tax credit investments
Held-to-maturity
Amortized cost	287	421
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Held-to-maturity	287	421
Obligations of state and political subdivisions
Held-to-maturity
Amortized cost	38,707	40,203
Gross unrealized gains	770	968
Gross unrealized losses	(102)	(2)
Held-to-maturity	$ 39,375	$ 41,169

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

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 securities classified as available-for-sale.

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

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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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