Related party transactions - Schedule of Income or Expenses with Related Parties (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Arrangement Fees [Member]
Related Party Transaction [Line Items]
Expenses incurred with related parties	$ 0	$ 1,827	$ 7,598
Transaction Fees [Member]
Related Party Transaction [Line Items]
Expenses incurred with related parties	0	2,262	6,317
Management Fees [Member]
Related Party Transaction [Line Items]
Income earned from related parties	914	4,447	4,266
Supervision Fees [Member]
Related Party Transaction [Line Items]
Income earned from related parties	0	1,300	7,800
Interest Expense [Member]
Related Party Transaction [Line Items]
Expenses incurred with related parties	19,380	0	0
Interest Income [Member]
Related Party Transaction [Line Items]
Income earned from related parties	$ 427	$ 2,677	$ 7,513

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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+ References

No definition available.

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- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

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