Financial Instruments - Summary of Bond Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair value at beginning of period	$ 38,399	$ 30,011
Purchases	15,429	14,089
Sales	(987)	(245)
Maturities and calls	(9,677)	(6,426)
Increase in bond premium	172	1,155
Fair market value adjustment	(194)	(185)
Fair value at end of period	$ 43,142	$ 38,399