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
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	$ 997,452	$ 210,981
Other comprehensive income (loss) before reclassifications, net of tax	166,988	405,653
Reclassifications, net of tax	1,201	(10,576)
Other comprehensive income (loss)	168,189	395,077
Accumulated other comprehensive income (loss), Ending Balance	1,165,641	606,058
Available for Sale Assets [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	1,090,273	256,196
Other comprehensive income (loss) before reclassifications, net of tax	172,409	409,139
Reclassifications, net of tax	(1,164)	(12,249)
Other comprehensive income (loss)	171,245	396,890
Accumulated other comprehensive income (loss), Ending Balance	1,261,518	653,086
Deferred Acquisition Costs [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	(10,758)	(6,728)
Other comprehensive income (loss) before reclassifications, net of tax	424	(2,748)
Reclassifications, net of tax	0	0
Other comprehensive income (loss)	424	(2,748)
Accumulated other comprehensive income (loss), Ending Balance	(10,334)	(9,476)
Foreign Exchange [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	17,386	24,866
Other comprehensive income (loss) before reclassifications, net of tax	(5,962)	(738)
Reclassifications, net of tax	0	0
Other comprehensive income (loss)	(5,962)	(738)
Accumulated other comprehensive income (loss), Ending Balance	11,424	24,128
Pension adjustments [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	(99,449)	(63,353)
Other comprehensive income (loss) before reclassifications, net of tax	117	0
Reclassifications, net of tax	2,365	1,673
Other comprehensive income (loss)	2,482	1,673
Accumulated other comprehensive income (loss), Ending Balance	$ (96,967)	$ (61,680)