Accumulated Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income, Beginning balance			$ 490,782	$ 413,712
Amounts reclassified from AOCI, net of tax expense (benefit)			(10,719)	(14,387)
Unrealized holding gains (losses) arising during the period net of tax expense (benefit)			(125,888)	121,782
Unrealized adjustment to DAC, net of tax expense (benefit)			19,259	(10,650)
Unrealized gains on investments attributable to participating policyholders' interest, net of tax expense (benefit)			4,694	(5,542)
Foreign currency adjustment, net of tax benefit	$ (1,437)	$ (476)	(2,087)	(577)
Accumulated Other Comprehensive Income, Ending balance	376,041	504,338	376,041	504,338
Net Unrealized Gains (Losses) on Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income, Beginning balance			568,151	457,937
Amounts reclassified from AOCI, net of tax expense (benefit)			(15,268)	(16,539)
Unrealized holding gains (losses) arising during the period net of tax expense (benefit)			(125,888)	121,782
Unrealized adjustment to DAC, net of tax expense (benefit)			19,259	(10,650)
Unrealized gains on investments attributable to participating policyholders' interest, net of tax expense (benefit)			4,694	(5,542)
Accumulated Other Comprehensive Income, Ending balance	450,948	546,988	450,948	546,988
Defined Benefit Pension Plan Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income, Beginning balance			(76,074)	(43,884)
Amounts reclassified from AOCI, net of tax expense (benefit)			4,549	2,152
Accumulated Other Comprehensive Income, Ending balance	(71,525)	(41,732)	(71,525)	(41,732)
Foreign Currency Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income, Beginning balance			(1,295)	(341)
Foreign currency adjustment, net of tax benefit			(2,087)	(577)
Accumulated Other Comprehensive Income, Ending balance	$ (3,382)	$ (918)	$ (3,382)	$ (918)