Income taxes (Tables)

9 Months Ended

Sep. 30, 2017

Income Tax Disclosure [Abstract]

Provision for income taxes

Provision for income taxes is based on the following:

	For Three Months Ended						For Nine Months Ended
	September 30,						September 30,
	2017			2016			2017			2016
Taxes calculated using the estimated annual effective tax rate	$	542		$	418		$	1,382		$	1,024
Discrete tax items		(38	)		(55	)		(190	)		(139	)
Provision for income taxes	$	504		$	363		$	1,192		$	885
Estimated annual effective tax rate		31	%		30	%		31	%		30	%
Actual effective tax rate		28	%		26	%		26	%		26	%