Summary of significant accounting policies - Additional Disclosures (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Accounting Policies [Abstract]
Credit value adjustment, percentage of fair value of derivatives for Level 3 classification greater than	10.00%
Marketing costs \| $	$ 45,020	$ 41,590	$ 38,361
Number of properties in Mexico for which local currency is not applicable \| property	1

Expenditures for planning and executing the conception, pricing, promotion, and distribution of ideas, goods, and services. Costs of public relations and corporate promotions are typically considered to be marketing costs.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Name:	us-gaap_MarketingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration