Fair value measurements (Tables)

12 Months Ended

Dec. 31, 2016

Fair Value Disclosures [Abstract]

Financial Instruments Measured at Fair Value on Recurring Basis

At December 31, 2016, financial instruments measured at fair value on a recurring basis are summarized below:

	Level 1	Level 2	Level 3	Fair value measurements
	($000 omitted)
Investments available-for-sale:
Debt securities:
Municipal	—	72,432	—	72,432
Corporate	—	343,047	—	343,047
Foreign	—	167,027	—	167,027
U.S. Treasury Bonds	—	12,613	—	12,613
Equity securities:	36,384	—	—	36,384
	36,384	595,119	—	631,503

At December 31, 2015, financial instruments measured at fair value on a recurring basis are summarized below:

	Level 1	Level 2	Level 3	Fair value measurements
	($000 omitted)
Investments available-for-sale:
Debt securities:
Municipal	—	72,008	—	72,008
Corporate	—	309,461	—	309,461
Foreign	—	153,221	—	153,221
U.S. Treasury Bonds	—	13,906	—	13,906
Equity securities:	31,253	—	—	31,253
	31,253	548,596	—	579,849