Income taxes (Tables)

6 Months Ended

Jun. 30, 2017

Income Tax Disclosure [Abstract]

Provision for income taxes

Provision for income taxes is based on the following:

	For Three Months Ended						For Six Months Ended
	June 30,						June 30,
	2017			2016			2017			2016
Taxes calculated using the estimated annual effective tax rate	$	458		$	325		$	840		$	606
Discrete tax items		(28	)		(42	)		(152	)		(84	)
Provision for income taxes	$	430		$	283		$	688		$	522
Estimated annual effective tax rate		31	%		30	%		31	%		30	%
Actual effective tax rate		29	%		26	%		25	%		25	%