Accumulated Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in accumulated other comprehensive income by component
Balance	$ 2,537,801
Other comprehensive income (loss)	87,024	$ (15,289)	$ 17,562
Amounts reclassified from accumulated other comprehensive income (loss)	391	668	1,038
Total other comprehensive income (loss), net of tax	87,415	(14,621)	18,600
Balance	5,707,015	2,537,801
Net Unrealized Gains (Losses) on Debt Securities Available for Sale and Interest-Only Strips
Changes in accumulated other comprehensive income by component
Balance	(28,022)	(16,353)	(28,601)
Other comprehensive income (loss)	83,696	(12,371)	15,387
Amounts reclassified from accumulated other comprehensive income (loss)	424	702	1,067
Total other comprehensive income (loss), net of tax	84,120	(11,669)	16,454
Reclassification of stranded tax effects from AOCI to retained earnings			(4,206)
Balance	56,098	(28,022)	(16,353)
Net Unrealized Gains (Losses) on Net Investment Hedges
Changes in accumulated other comprehensive income by component
Balance	14,986	4,536	6,493
Other comprehensive income (loss)	(5,186)	10,450	(2,746)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Total other comprehensive income (loss), net of tax	(5,186)	10,450	(2,746)
Reclassification of stranded tax effects from AOCI to retained earnings			789
Balance	9,800	14,986	4,536
Foreign Currency Translation Adjustment
Changes in accumulated other comprehensive income by component
Balance	(20,211)	(6,843)	(11,764)
Other comprehensive income (loss)	8,514	(13,368)	4,921
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Total other comprehensive income (loss), net of tax	8,514	(13,368)	4,921
Reclassification of stranded tax effects from AOCI to retained earnings			0
Balance	(11,697)	(20,211)	(6,843)
Recognized Postretirement Prior Service Cost
Changes in accumulated other comprehensive income by component
Balance	109	143	147
Other comprehensive income (loss)	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	(33)	(34)	(29)
Total other comprehensive income (loss), net of tax	(33)	(34)	(29)
Reclassification of stranded tax effects from AOCI to retained earnings			25
Balance	76	109	143
AOCI Attributable to Parent
Changes in accumulated other comprehensive income by component
Balance	(33,138)	(18,517)	(33,725)
Total other comprehensive income (loss), net of tax	87,415	(14,621)	18,600
Reclassification of stranded tax effects from AOCI to retained earnings			(3,392)
Balance	$ 54,277	$ (33,138)	$ (18,517)