Reconciliation of Asset Retirement Obligations which are Included in Other Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 5,890	$ 6,437
Changes in estimates	172	112
Liabilities incurred	110	238
Liabilities settled	0	(92)
Sale of properties	(3,932)	(1,224)
Accretion expense	381	419
Balance at end of year	$ 2,621	$ 5,890