Fair Value - Fair Value Measurements on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - Fair Value on Recurring Basis - Significant Unobservable Inputs (Level 3) - Industrial revenue bonds - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 3,437	$ 3,690
Principal reduction	(170)	(170)
Included in other comprehensive income	(18)	17
Ending balance	$ 3,249	$ 3,537