Investments - Schedule of Securities in Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	$ 487,359
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(15,474)
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, fair value	38,141
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	(1,198)
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	436,601	$ 98,019
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(15,473)	(2,292)
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, fair value	38,141	18,144
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	(1,198)	(991)
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	50,758
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(1)
U.S. Government and Agencies [Member] | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	1,594	1,619
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(20)	(3)
U.S. Government and Agencies [Member] | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	50,758
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(1)
Foreign Government [Member] | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	27,174	4,034
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(2,267)	(39)
States and Political Subdivisions [Member] | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	24,656	449
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(777)	(1)
Corporates [Member] | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	306,273	68,057
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(11,344)	(1,628)
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, fair value	28,946	11,964
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	(985)	(917)
Residential Mortgage-backed Securities [Member] | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	22,400	1,672
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(304)	(35)
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, fair value	1,782	862
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	(57)	(19)
Commercial Mortgage-backed Securities [Member] | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	41,870	10,200
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(641)	(50)
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, fair value	207	2,168
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	(3)	(6)
Other Asset-backed Securities [Member] | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, fair value	12,634	11,988
Available-for-sale securities, continuous unrealized loss position, less than 12 months, aggregate losses	(120)	(536)
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, fair value	7,206	3,150
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	$ (153)	$ (49)