SIGNIFICANT TRANSACTIONS - USWC Holding Company Acquisition (Details) - USD ($) $ in Thousands		11 Months Ended	12 Months Ended
	Dec. 01, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2017
Assets
Goodwill			$ 793,470	$ 793,470
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Intangible assets subject to amortization	$ 70,400
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
2017				56,011
2018				52,898
2019				49,897
2020				48,105
2021				$ 45,771
Distribution Relationships
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Intangible assets subject to amortization	65,000
Trade names
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Intangible assets subject to amortization	1,400
Technology
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Intangible assets subject to amortization	$ 4,000
USWC
Business Acquisition [Line Items]
Percent of outstanding shares acquired	100.00%
Purchase price	$ 136,100
Assets
Fixed maturities	10,592
Other long-term investments	2,340
Cash	122,167
Accrued investment income	52
Accounts and premiums receivable	18,536
Reinsurance receivables	9,397
Value of businesses acquired	5,079
Goodwill	61,027
Other intangibles	70,400
Property and equipment	390
Accrued income taxes	4,161
Other assets	40
Total assets	304,181
Liabilities
Unearned premiums	82,757
Other policyholders' funds	21,483
Other liabilities	24,951
Deferred income taxes	38,929
Total liabilities	168,120
Net assets acquired	136,061
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
2017	4,843
2018	4,843
2019	4,843
2020	4,843
2021	$ 4,843
Pro forma condensed consolidated results of operations
Revenue		$ 3,753,700	4,532,292
Net income		$ 268,479	393,277
Revenue recognized in earnings			4,700
Net income recognized in earnings			$ 200
USWC | Minimum | Distribution Relationships
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Weighted-average useful life of intangible assets acquired	13 years
USWC | Minimum | Trade names
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Weighted-average useful life of intangible assets acquired	5 years
USWC | Minimum | Technology
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Weighted-average useful life of intangible assets acquired	8 years
USWC | Maximum | Distribution Relationships
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Weighted-average useful life of intangible assets acquired	21 years
USWC | Maximum | Trade names
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Weighted-average useful life of intangible assets acquired	6 years
USWC | Maximum | Technology
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [Abstract]
Weighted-average useful life of intangible assets acquired	11 years