Fair Values of Financial Instruments - Reconciliation of Beginning and Ending Balances of Recurring Fair Value Measurements using Significant Unobservable Level 3 Inputs (Detail) (Fair Value, Measurements, Recurring, Available for Sale Securities, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Measurements, Recurring | Available for Sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 9,977	$ 18,328
Included in other comprehensive income	3,656	1,330
Purchases, issuances, and settlements		7,590
Transfers in/(out) of Level 3		(16,434)
Principal (payments)/additions	(6,987)	(837)
Ending balance	$ 6,646	$ 9,977