Income taxes (Tables)

6 Months Ended

Jun. 30, 2018

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit)

	Three months ended June 30,						Six months ended June 30,
(dollars in thousands)	2018			2017			2018			2017
Income tax (benefit) expense	$	706		$	1,991		$	(2,076	)	$	24,273
Effective tax rate	(1.9		)%	(7.0		)%	1.8		%	(20.7		)%