Bank segment - Components of investment securities (Details) $ in Thousands	Sep. 30, 2017 USD ($) issue	Dec. 31, 2016 USD ($) issue
Available-for-sale securities
Amortized cost	$ 1,329,207	$ 1,118,350
Gross unrealized gains	3,009	2,662
Gross unrealized losses	(12,106)	(15,830)
Available-for-sale investment securities	$ 1,320,110	$ 1,105,182
Available-for-sale Securities, Continuous Unrealized Loss Position
Available-for-sale, securities, less than 12 months, number of issues (in issues) \| issue	99	106
Fair value, less than 12 months	$ 777,389	$ 833,130
Gross unrealized losses, less than 12 months	$ (8,773)	$ (14,153)
Available-for-sale, securities, greater than 12 months, number of issues (in issues) \| issue	31	14
Fair value, 12 months or longer	$ 151,123	$ 50,970
Gross unrealized losses, 12 months or longer	(3,333)	(1,677)
U.S. Treasury and federal agency obligations
Available-for-sale securities
Amortized cost	182,535	193,515
Gross unrealized gains	882	920
Gross unrealized losses	(1,299)	(2,154)
Available-for-sale investment securities	$ 182,118	$ 192,281
Available-for-sale Securities, Continuous Unrealized Loss Position
Available-for-sale, securities, less than 12 months, number of issues (in issues) \| issue	15	18
Fair value, less than 12 months	$ 91,203	$ 123,475
Gross unrealized losses, less than 12 months	$ (1,064)	$ (2,010)
Available-for-sale, securities, greater than 12 months, number of issues (in issues) \| issue	2	1
Fair value, 12 months or longer	$ 13,072	$ 3,485
Gross unrealized losses, 12 months or longer	(235)	(144)
Mortgage-related securities- FNMA, FHLMC and GNMA
Available-for-sale securities
Amortized cost	1,131,245	909,408
Gross unrealized gains	2,127	1,742
Gross unrealized losses	(10,807)	(13,676)
Available-for-sale investment securities	$ 1,122,565	$ 897,474
Available-for-sale Securities, Continuous Unrealized Loss Position
Available-for-sale, securities, less than 12 months, number of issues (in issues) \| issue	84	88
Fair value, less than 12 months	$ 686,186	$ 709,655
Gross unrealized losses, less than 12 months	$ (7,709)	$ (12,143)
Available-for-sale, securities, greater than 12 months, number of issues (in issues) \| issue	29	13
Fair value, 12 months or longer	$ 138,051	$ 47,485
Gross unrealized losses, 12 months or longer	(3,098)	(1,533)
Mortgage revenue bond
Available-for-sale securities
Amortized cost	15,427	15,427
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Available-for-sale investment securities	$ 15,427	$ 15,427
Available-for-sale Securities, Continuous Unrealized Loss Position
Available-for-sale, securities, less than 12 months, number of issues (in issues) \| issue	0	0
Fair value, less than 12 months	$ 0	$ 0
Gross unrealized losses, less than 12 months	$ 0	$ 0
Available-for-sale, securities, greater than 12 months, number of issues (in issues) \| issue	0	0
Fair value, 12 months or longer	$ 0	$ 0
Gross unrealized losses, 12 months or longer	$ 0	$ 0

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

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-Publisher FASB
-Name Accounting Standards Codification
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