Stock-based compensation (Tables)

6 Months Ended

Jun. 30, 2018

Executive Officers

Schedule of Unvested Restricted Stock Units Roll Forward [Table Text Block]

(Not in thousands)	Shares		Weighted-Average Grant Date Fair Value
Non-vested at December 31, 2016	383,982	$	26.35
Granted	212,200		42.57
Performance Shares Quantity Adjustment	(232,989)		29.10
Vested	(67,853)		48.54
Non-vested at December 31, 2017	295,340	$	30.75
Granted	227,720		45.48
Performance Shares Quantity Adjustment	160,693		30.24
Vested	(280,733)		34.48
Forfeited	(2,326)		33.07
Non-vested at June 30, 2018	400,694	$	36.29

Directors

Schedule of Unvested Restricted Stock Units Roll Forward [Table Text Block]

(Not in thousands)	Restricted Stock		Weighted-Average Grant Date Fair Value
Non-vested at December 31, 2016	-	$	-
Granted	25,771		38.42
Vested	(25,771)		38.42
Forfeited	-		-
Non-vested at December 31, 2017	-	$	-
Granted	22,394		46.90
Vested	(22,394)		46.90
Forfeited	-		-
Non-vested at June 30, 2018	-	$	-