Accumulated Other Comprehensive Income - Changes in AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Changes in AOCI by component
Beginning Balance	$ 4,862,576	$ 5,137,014	$ 4,900,189
OCI before reclassifications	(3,101)	(6,939)	(6,125)
Amounts reclassified from AOCI	61	0	(1,603)
Net period OCI	(3,040)	(6,939)	(7,728)
Ending Balance	6,433,892	4,862,576	5,137,014
Cumulative Unrealized Gain (Loss) on Available-for- Sale Securities
Changes in AOCI by component
Beginning Balance	44,057	50,996	53,515
OCI before reclassifications	(3,101)	(6,939)	(2,460)
Amounts reclassified from AOCI	(3)	0	(59)
Net period OCI	(3,104)	(6,939)	(2,519)
Ending Balance	40,953	44,057	50,996
Foreign Currency Translation
Changes in AOCI by component
Beginning Balance	(64)	(64)	5,145
OCI before reclassifications	0	0	(3,665)
Amounts reclassified from AOCI	64	0	(1,544)
Net period OCI	64	0	(5,209)
Ending Balance	0	(64)	(64)
Accumulated Other Comprehensive Income
Changes in AOCI by component
Beginning Balance	43,993	50,932	58,660
Ending Balance	$ 40,953	$ 43,993	$ 50,932