Revenue from Contracts with Customers - Summary of Disaggregation of Revenues from Contracts (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		$ 637,711	$ 524,936
Term Life Insurance Segment [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		382,027	327,746
Term Life Insurance Segment [Member] | Total Segment Revenues from Contracts with Customers [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		11,810	10,168
Term Life Insurance Segment [Member] | Total Segment Revenues from Contracts with Customers [Member] | Other, Net [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		11,810	10,168
Term Life Insurance Segment [Member] | Revenues from Sources Other Than Contracts with Customers (Segregated Funds) [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		370,217	317,578
Investment and Savings Products Segment [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		223,422	185,032
Investment and Savings Products Segment [Member] | Total Segment Revenues from Contracts with Customers [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		207,794	170,631
Investment and Savings Products Segment [Member] | Total Segment Revenues from Contracts with Customers [Member] | Other, Net [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		2,949	2,542
Investment and Savings Products Segment [Member] | Total Segment Revenues from Contracts with Customers [Member] | Commissions and Fees [Member] | Sales-based Revenues [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		98,112	80,891
Investment and Savings Products Segment [Member] | Total Segment Revenues from Contracts with Customers [Member] | Commissions and Fees [Member] | Asset-based Revenues [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		85,613	66,994
Investment and Savings Products Segment [Member] | Total Segment Revenues from Contracts with Customers [Member] | Commissions and Fees [Member] | Account-based Revenues [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		21,120	20,204
Investment and Savings Products Segment [Member] | Revenues from Sources Other Than Contracts with Customers (Segregated Funds) [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		15,628	14,401
Corporate and Other Distributed Products Segment [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		32,262	12,158
Corporate and Other Distributed Products Segment [Member] | Total Segment Revenues from Contracts with Customers [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		14,407	8,534
Corporate and Other Distributed Products Segment [Member] | Total Segment Revenues from Contracts with Customers [Member] | Other, Net [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		836	955
Corporate and Other Distributed Products Segment [Member] | Total Segment Revenues from Contracts with Customers [Member] | Commissions and Fees [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers	[1]	13,571	7,579
Corporate and Other Distributed Products Segment [Member] | Revenues from Sources Other Than Contracts with Customers (Segregated Funds) [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenues from contracts with customers		$ 17,855	$ 3,624

[1] Commissions and fees included $1.1 million for the three months ended March 31, 2021 and 2020, attributable to performance obligations satisfied in a previous reporting period and represent the collection of variable consideration in the transaction price that had been previously constrained.