Goodwill and other intangibles - Summary of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Goodwill summary
Beginning balances	$ 231,428	$ 217,094
Acquisitions	17,504	14,419
Disposals	(42)	(85)
Ending balances	248,890	231,428
Title
Goodwill summary
Beginning balances	225,699	211,365
Acquisitions	17,504	14,419
Disposals	(42)	(85)
Ending balances	243,161	225,699
Ancillary Services and Corporate
Goodwill summary
Beginning balances	5,729	5,729
Acquisitions	0	0
Disposals	0	0
Ending balances	$ 5,729	$ 5,729

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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-Section 45
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-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

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- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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-Publisher FASB
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-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
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