Loan Servicing - Originated Mortgage Servicing Rights (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Payments for (Proceeds from) Mortgage Servicing Rights [Abstract]
Balances, January 1	$ 11,681	$ 9,271	$ 7,980
Servicing rights capitalized	2,109	3,426	2,974
Amortization of servicing rights	(1,601)	(1,016)	(1,683)
Balances, December 31	12,189	11,681	9,271
Balances, January 1	(507)	(397)	(338)
Additions	(85)	(236)	(130)
Reductions	5	126	71
Balances, December 31	(587)	(507)	(397)
Mortgage servicing rights, net	$ 11,602	$ 11,174	$ 8,874

The periodic amortization (in proportion to and over the period of estimated net servicing income or loss) of capitalized servicing rights, which contractually entitle the servicer to receive fees and ancillary revenues for performing billing, collection, disbursement and recordkeeping services in connection with a mortgage portfolio. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 4
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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