Segment and Geographical Information - Summary of Assets and Profit or Loss by Segment (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues		$ 637,711	$ 524,936
Net investment income		20,052	15,420
Amortization of deferred policy acquisition costs		66,105	70,311
Non-cash share-based compensation expense		11,653	11,161
Income (loss) before income taxes		128,309	94,546
Assets		15,113,860		$ 14,905,285
Term Life Insurance Segment [Member]
Segment Reporting Information [Line Items]
Revenues		382,027	327,746
Net investment income		8,253	6,246
Amortization of deferred policy acquisition costs		62,584	65,840
Non-cash share-based compensation expense		1,988	1,786
Income (loss) before income taxes		88,236	82,892
Assets		7,135,875		6,985,086
Investment and Savings Products Segment [Member]
Segment Reporting Information [Line Items]
Revenues		223,422	185,032
Amortization of deferred policy acquisition costs		3,275	4,305
Non-cash share-based compensation expense		1,208	1,105
Income (loss) before income taxes		63,363	47,700
Assets	[1]	2,758,276		2,769,445
Corporate and Other Distributed Products Segment [Member]
Segment Reporting Information [Line Items]
Revenues		32,262	12,158
Net investment income		11,799	9,174
Amortization of deferred policy acquisition costs		246	166
Non-cash share-based compensation expense		8,457	8,270
Income (loss) before income taxes		(23,290)	$ (36,046)
Assets		$ 5,219,709		$ 5,150,754

[1] The Investment and Savings Products segment includes assets held in separate accounts. Excluding separate accounts, the Investment and Savings Products segment assets were $119.4 million and $110.0 million as of March 31, 2021 and December 31, 2020, respectively.