Fair value measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Financial instruments measured at fair value on recurring basis

At December 31, 2017, 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	—	72,669	—	72,669
Corporate	—	357,933	—	357,933
Foreign	—	228,237	—	228,237
U.S. Treasury Bonds	—	12,602	—	12,602
Equity securities:	37,914	—	—	37,914
	37,914	671,441	—	709,355

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