Allowance for Expected Credit Losses Balances of Premiums Receivable (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Balance, beginning of period	$ 199,356	$ 193,369
Balance, end of period	193,967	193,967
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	914	578
Current period change for expected credit losses	296	2,498
Writeoffs of uncollectable accounts receivable	(251)	(2,117)
Balance, end of period	$ 959	$ 959