Business Segment Information (Narrative) (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 475,651,000	$ 400,646,000	$ 931,337,000	$ 815,408,000
Intersegment
Segment Reporting Information [Line Items]
Revenues	$ 0	$ 0	$ 0	$ 0

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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+ Details