Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Change in Balance by Component of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning Balance	$ 606,058	$ 850,030	$ 210,981	[1]	$ 925,275
Other comprehensive income (loss) before reclassifications, net of tax	282,124	(514,224)	687,777		(594,091)
Reclassifications, net of tax	(208)	(1,906)	(10,784)		2,716
Other comprehensive income (loss)	281,916	(516,130)	676,993		(591,375)
Accumulated other comprehensive income (loss), Ending Balance	887,974	333,900	887,974		333,900
Pension adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning Balance	(61,680)	(106,331)	(63,353)		(109,283)
Other comprehensive income (loss) before reclassifications, net of tax	297	0	297		0
Reclassifications, net of tax	1,673	2,997	3,346		5,949
Other comprehensive income (loss)	1,970	2,997	3,643		5,949
Accumulated other comprehensive income (loss), Ending Balance	(59,710)	(103,334)	(59,710)		(103,334)
Foreign Exchange [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning Balance	24,128	25,859	24,866		26,608
Other comprehensive income (loss) before reclassifications, net of tax	1,996	(3,077)	1,258		(3,826)
Reclassifications, net of tax	0	0	0		0
Other comprehensive income (loss)	1,996	(3,077)	1,258		(3,826)
Accumulated other comprehensive income (loss), Ending Balance	26,124	22,782	26,124		22,782
Deferred Acquisition Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning Balance	(9,476)	(14,495)	(6,728)		(16,417)
Other comprehensive income (loss) before reclassifications, net of tax	(1,979)	4,944	(4,727)		6,866
Reclassifications, net of tax	0	0	0		0
Other comprehensive income (loss)	(1,979)	4,944	(4,727)		6,866
Accumulated other comprehensive income (loss), Ending Balance	(11,455)	(9,551)	(11,455)		(9,551)
Available for Sale Assets [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning Balance	653,086	944,997	256,196		1,024,367
Other comprehensive income (loss) before reclassifications, net of tax	281,810	(516,091)	690,949		(597,131)
Reclassifications, net of tax	(1,881)	(4,903)	(14,130)		(3,233)
Other comprehensive income (loss)	279,929	(520,994)	676,819		(600,364)
Accumulated other comprehensive income (loss), Ending Balance	$ 933,015	$ 424,003	$ 933,015		$ 424,003

[1] Derived from audited financial statements