New accounting pronouncement benefit plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other components of net periodic benefit income	$ 1,705	$ 1,448	$ 3,410	$ 2,896
Total other income	23,242	20,699	50,145	39,654
Employee Benefits and Share-based Compensation	7,630	6,206	14,659	12,674
Other Cost and Expense, Operating	1,665	1,749	3,575	3,405
Total other expense	$ 52,534	$ 49,554	$ 106,842	$ 98,464