Fair Value (Activity Under Level 3, Fair Value Measurements Using Significant Unobservable Inputs By Asset Type) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 87,124	$ 16,302	$ 67,735	$ 5,526
Total gains or (losses) (realized/unrealized), Included in earnings	839	(18)	1,029	(1,007)
Total gains or (losses) (realized/unrealized), Included in other comprehensive income (loss)	172	1,398	143	1,392
Purchases, issuances and settlements	1,156	16,749	20,384	28,520
Transfers in and/or (out) of Level 3
Ending balance	89,291	34,431	89,291	34,431
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at the reporting date				(997)
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	84,322	15,706	65,197	3,933
Total gains or (losses) (realized/unrealized), Included in earnings	711	(18)	925	(10)
Total gains or (losses) (realized/unrealized), Included in other comprehensive income (loss)	172	(27)	143	(33)
Purchases, issuances and settlements	935	16,749	19,875	28,520
Transfers in and/or (out) of Level 3
Ending balance	86,140	32,410	86,140	32,410
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at the reporting date
Foreign Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	2,802	596	2,538	1,593
Total gains or (losses) (realized/unrealized), Included in earnings	128		104	(997)
Total gains or (losses) (realized/unrealized), Included in other comprehensive income (loss)		1,425		1,425
Purchases, issuances and settlements	221		509
Transfers in and/or (out) of Level 3
Ending balance	3,151	$ 2,021	3,151	2,021
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at the reporting date				$ (997)