New accounting pronouncement benefit plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other components of net periodic benefit income	$ 1,705	$ 1,448
Total other income	26,903	18,955
Employee Benefits and Share-based Compensation	7,029	6,468
Other Cost and Expense, Operating	1,910	1,656
Total other expense	$ 54,308	48,910
AccountingStandardsUpdate201707 [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other components of net periodic benefit income		0
Total other income		17,507
Employee Benefits and Share-based Compensation		5,181
Other Cost and Expense, Operating		1,495
Total other expense		47,462
AccountingStandardsUpdate201707 [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other components of net periodic benefit income		1,448
Total other income		18,955
Employee Benefits and Share-based Compensation		6,468
Other Cost and Expense, Operating		1,656
Total other expense		$ 48,910