Segment and Geographical Information - Summary of Assets and Profit or Loss by Segment (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues		$ 525,815	$ 504,902	$ 1,050,751	$ 999,890
Net investment income		22,710	24,868	38,130	48,980
Amortization of deferred policy acquisition costs		53,177	58,762	123,488	123,390
Non-cash share-based compensation expense		2,357	2,103	13,518	12,987
Income (loss) before income taxes		134,062	127,460	228,607	229,828
Assets		13,964,549		13,964,549		$ 13,688,531
Term Life Insurance Segment [Member]
Segment Reporting Information [Line Items]
Revenues		328,233	296,868	655,979	593,712
Net investment income		6,538	4,736	12,785	9,180
Amortization of deferred policy acquisition costs		52,730	56,179	118,571	120,245
Non-cash share-based compensation expense		679	617	2,466	2,489
Income (loss) before income taxes		94,904	83,997	177,794	154,337
Assets		6,735,121		6,735,121		6,546,129
Investment and Savings Products Segment [Member]
Segment Reporting Information [Line Items]
Revenues		164,181	173,086	349,213	335,756
Amortization of deferred policy acquisition costs		100	2,101	4,405	2,578
Non-cash share-based compensation expense		658	666	1,763	2,121
Income (loss) before income taxes		46,860	47,343	94,559	90,026
Assets	[1]	2,493,939		2,493,939		2,598,493
Corporate and Other Distributed Products Segment [Member]
Segment Reporting Information [Line Items]
Revenues		33,401	34,948	45,559	70,422
Net investment income		16,172	20,132	25,345	39,800
Amortization of deferred policy acquisition costs		347	482	512	567
Non-cash share-based compensation expense		1,020	820	9,289	8,377
Income (loss) before income taxes		(7,702)	$ (3,880)	(43,746)	$ (14,535)
Assets		$ 4,735,489		$ 4,735,489		$ 4,543,909

[1] The Investment and Savings Products segment includes assets held in separate accounts. Excluding separate accounts, the Investment and Savings Products segment assets were $116.3 million and $112.8 million as of June 30, 2020 and December 31, 2019, respectively.