Income taxes - Schedule of Allocation of Federal and State Income Taxes between Current and Deferred Portions (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current	$ 19,259	$ 14,629	$ 12,476
Deferred	6,359	6,458	9,257
Total	$ 25,618	$ 21,087	$ 21,733

Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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