Mortgage Servicing Rights - Changes in the Company's MSRs (Details) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Changes in mortgage servicing rights
Balance at January 1, 2018	$ 39,339
Capitalization	10,745
Amortization	(3,671)
Balance at September 30, 2018	$ 46,413

Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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Name:	us-gaap_ServicingAssetAtAmortizedValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant