Goodwill and Other Intangible Assets - Reconciliation of Goodwill and Other Indefinite Lived Intangibles (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill beginning balance	$ 625,675	$ 628,877
Goodwill attributable to certain insurance business lines sold during 2014	(4,482)
Deferred tax purchase accounting adjustment made during the period		(3,202)
Goodwill ending balance	$ 621,193	$ 625,675