Accumulated Other Comprehensive Income (Loss) (Components of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Before-Tax
Net change, other comprehensive income (loss)	$ 40,095	$ (19,374)	$ 72,652	$ (39,282)
Tax Effect
Net change, other comprehensive income (loss)	(17,084)	3,711	(24,450)	11,605
Net-of-Tax
Other comprehensive income (loss)	23,011	(15,663)	48,202	(27,677)
Available- for-Sale Investment Securities
Before-Tax
Net unrealized gains (losses) arising during the period	44,531	(12,342)	75,469	(36,919)
Net realized gains reclassified into net income	(1,447)	(210)	(3,008)	(2,339)
Net change, other comprehensive income (loss)	43,084	(12,552)	72,461	(39,258)
Tax Effect
Net unrealized gains (losses) arising during the period	(14,485)	3,649	(22,312)	10,915
Net realized gains reclassified into net income	428	62	889	690
Net change, other comprehensive income (loss)	(14,057)	3,711	(21,423)	11,605
Net-of-Tax
Net unrealized gains (losses) arising during the period	30,046	(8,693)	53,157	(26,004)
Net realized gains reclassified into net income	(1,019)	(148)	(2,119)	(1,649)
Other comprehensive income (loss)	29,027	(8,841)	51,038	(27,653)
Foreign Currency Translation Adjustments
Before-Tax
Net unrealized gains (losses) arising during the period	(2,989)	(6,822)	191	(24)
Net change, other comprehensive income (loss)	(2,989)	(6,822)	191	(24)
Tax Effect
Net unrealized gains (losses) arising during the period	(3,027)	0	(3,027)	0
Net change, other comprehensive income (loss)	(3,027)	0	(3,027)	0
Net-of-Tax
Net unrealized gains (losses) arising during the period	(6,016)	(6,822)	(2,836)	(24)
Net realized gains reclassified into net income	0	0	0	0
Other comprehensive income (loss)	$ (6,016)	$ (6,822)	$ (2,836)	$ (24)