Debt (Tables)

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Abstract]

Schedule of Long-term Debt Instruments [Table Text Block]

The Company’s long-term debt consists of the following as of December 31, 2018 and 2017 (dollars in thousands):

	2018			2017
$400 million 6.45% Senior Notes due 2019	$	399,941		$	399,873
$400 million 5.00% Senior Notes due 2021	399,466			399,245
$400 million 4.70% Senior Notes due 2023	399,288			399,138
$400 million 3.95% Senior Notes due 2026	399,988			399,987
$100 million 4.09% Promissory Note due 2039	89,098			91,787
$400 million 6.20% Subordinated Debentures due 2042	400,000			400,000
$400 million 5.75% Subordinated Debentures due 2056	400,000			400,000
$400 million Variable Rate Junior Subordinated Debentures due 2065	318,743			318,740
Sub-total	2,806,524			2,808,770
Unamortized issuance costs	(18,651		)	(20,405		)
Long-term Debt	$	2,787,873		$	2,788,365

Schedule of Maturities of Long-term Debt [Table Text Block]

Future principal payments due on long-term debt, excluding discounts, as of December 31, 2018, were as follows (dollars in thousands):

	Calendar Year
	2019		2020		2021		2022		2023		Thereafter
Long-term debt	$	402,802	$	2,919	$	403,040	$	3,167	$	403,299	$	1,593,674

Schedule of Line of Credit Facilities [Table Text Block]

The following table provides additional information on the Company’s existing committed credit facilities as of December 31, 2018 and 2017 (dollars in thousands):

		Amount Utilized(1) December 31,
Current Capacity	Maturity Date	2018		2017		Basis of Fees
$191,583 (2)	March 2019	$	4,156	$	5,952	Fixed
188,000	November 2019	188,000		188,000		Fixed
105,735 (2)	December 2019	105,735		117,135		Fixed
100,000	June 2020	—		75,573		Fixed
100,000	May 2021	61,000		100,000		Fixed
75,000	June 2021	33,900		61,900		Fixed
500,000	May 2022	395,000		500,000		Debt rating and utilization %
850,000	August 2023	18,153		95,564		Senior unsecured long-term debt rating

(1) Represents issued but undrawn letters of credit. There was no cash borrowed for the periods presented.

(2) Foreign currency denominated facility, amounts presented are in U.S. dollars.