Summary of Significant Accounting Policies - Comprehensive Earnings - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
COMPREHENSIVE EARNINGS
Tax rate used (as a percent)	21.00%			21.00%			21.00%	21.00%
Other comprehensive income (loss), tax expense (benefit)	$ (3,200)			$ 2,500			$ (11,100)	$ 13,300
Changes in the balance of each component of accumulated other comprehensive earnings
Other comprehensive earnings (loss), net of tax	$ (12,240)	$ 15,177	$ (44,747)	$ 9,550	$ 53,571	$ (13,031)	$ (41,810)	$ 50,090

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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+ Details