Income taxes (Tables)

3 Months Ended

Mar. 31, 2017

Income Tax Disclosure [Abstract]

Provision for income taxes

Provision for income taxes is based on the following:

	For Three Months Ended
	March 31,
	2017			2016
Taxes calculated using the estimated annual effective tax rate	$	382		$	281
Discrete tax items		(124	)		(42	)
Provision for income taxes	$	258		$	239
Estimated annual effective tax rate		30	%		30	%
Actual effective tax rate		21	%		25	%