Mortgage servicing rights - Schedule of Servicing Income and Expense Included in Mortgage Banking Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Servicing income:
Servicing income	$ 4,052	$ 5,604	$ 8,803	$ 10,397
Change in fair value of mortgage servicing rights	(8,863)	(15)	(13,221)	3,528
Change in fair value of derivative hedging instruments	5,063	(1,763)	7,540	(7,019)
Servicing income	252	3,826	3,122	6,906
Servicing expenses	1,485	2,078	3,229	3,873
Net servicing (loss) income	$ (1,233)	$ 1,748	$ (107)	$ 3,033

All amounts that, per contract, are due to the servicer in exchange for servicing the financial asset and would no longer be received by a servicer if the beneficial owners of the serviced assets (or their trustees or agents) were to exercise their actual or potential authority under the contract to shift the servicing to another servicer. Depending on the servicing contract, those fees may include some or all of the difference between the interest rate collected on the asset being serviced and the rate to be paid to the beneficial owners of the asset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746

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Balance Type:	credit
Period Type:	duration