Supplemental balance sheet information (available-for-sale debt securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018		Dec. 31, 2017
Available-for-sale debt securities [Line Items]
Cost	$ 31,619		$ 34,306
Gross unrealized gains	0		0
Gross unrealized losses	(430)		(393)
Fair value	31,189		33,913
Cash	67,728		59,240
Expected maturities of available-for-sale debt securities
Due in one year or less	24,760
Due in two to five years	3,586
Due in six to ten years	2,843
Fair value	31,189		33,913
Funds held for customers [Member]
Available-for-sale debt securities [Line Items]
Cost	31,619	[1]	34,306	[2]
Gross unrealized gains	0	[1]	0	[2]
Gross unrealized losses	(430)	[1]	(393)	[2]
Fair value	31,189	[1]	33,913	[2]
Cash	63,751		52,279
Expected maturities of available-for-sale debt securities
Fair value	31,189	[1]	33,913	[2]
Funds held for customers [Member] | Money market securities [Member] | Domestic [Member]
Available-for-sale debt securities [Line Items]
Cost	15,000		17,300
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Fair value	15,000		17,300
Expected maturities of available-for-sale debt securities
Fair value	15,000		17,300
Funds held for customers [Member] | Canadian and provincial government securities [Member] | Canadian [Member]
Available-for-sale debt securities [Line Items]
Cost	8,867		9,051
Gross unrealized gains	0		0
Gross unrealized losses	(430)		(393)
Fair value	8,437		8,658
Expected maturities of available-for-sale debt securities
Fair value	8,437		8,658
Funds held for customers [Member] | Canadian guaranteed investment certificates [Member] | Canadian [Member]
Available-for-sale debt securities [Line Items]
Cost	7,752		7,955
Gross unrealized gains	0		0
Gross unrealized losses	0		0
Fair value	7,752		7,955
Expected maturities of available-for-sale debt securities
Fair value	$ 7,752		$ 7,955

[1] Funds held for customers, as reported on the consolidated balance sheet as of March 31, 2018, also included cash of $63,751.

[2] Funds held for customers, as reported on the consolidated balance sheet as of December 31, 2017, also included cash of $52,279.