Accumulated Other Comprehensive Income (Loss) - Rollforward of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Changes in accumulated other comprehensive income by component
Balance	$ 5,658,555	$ 2,710,517	$ 5,727,241	$ 2,556,260
Total other comprehensive income (loss), net of tax	(6,637)	18,894	137,494	89,366
Balance	5,658,420	5,693,417	5,658,420	5,693,417
Total
Changes in accumulated other comprehensive income by component
Balance	198,408	37,334	54,277	(33,138)
Other comprehensive income (loss)	(5,431)	18,303	136,800	88,912
Amounts reclassified from accumulated other comprehensive income (loss)	(1,206)	591	694	454
Total other comprehensive income (loss), net of tax	(6,637)	18,894	137,494	89,366
Balance	191,771	56,228	191,771	56,228
Net Unrealized Gains (Losses) on Available-for-Sale Investment Securities and Interest-only Strips
Changes in accumulated other comprehensive income by component
Balance	202,342	39,971	56,098	(28,022)
Other comprehensive income (loss)	(6,497)	18,630	137,829	86,744
Amounts reclassified from accumulated other comprehensive income (loss)	(1,197)	600	721	479
Total other comprehensive income (loss), net of tax	(7,694)	19,230	138,550	87,223
Balance	194,648	59,201	194,648	59,201
Net Unrealized Gains (Losses) on Net Investment Hedges
Changes in accumulated other comprehensive income by component
Balance	15,724	10,499	9,800	14,986
Other comprehensive income (loss)	(2,655)	1,641	3,269	(2,846)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0	0
Total other comprehensive income (loss), net of tax	(2,655)	1,641	3,269	(2,846)
Balance	13,069	12,140	13,069	12,140
Foreign Currency Translation Adjustment
Changes in accumulated other comprehensive income by component
Balance	(19,716)	(13,229)	(11,697)	(20,211)
Other comprehensive income (loss)	3,721	(1,968)	(4,298)	5,014
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0	0
Total other comprehensive income (loss), net of tax	3,721	(1,968)	(4,298)	5,014
Balance	(15,995)	(15,197)	(15,995)	(15,197)
Recognized Postretirement Prior Service Cost
Changes in accumulated other comprehensive income by component
Balance	58	93	76	109
Other comprehensive income (loss)	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	(9)	(9)	(27)	(25)
Total other comprehensive income (loss), net of tax	(9)	(9)	(27)	(25)
Balance	$ 49	$ 84	$ 49	$ 84