Income taxes (Tables)

3 Months Ended

Mar. 31, 2018

Income Tax Disclosure [Abstract]

Provision for income taxes

Provision for income taxes is based on the following:

	For Three Months Ended
	March 31,
	2018			2017
Taxes calculated using the estimated annual effective tax rate	$	316		$	382
Discrete tax items		(129	)		(124	)
Provision for income taxes	$	187		$	258
Estimated annual effective tax rate		20	%		30	%
Actual effective tax rate		12	%		21	%