Employee and Non-Employee Benefit Plans (Detail) - Net Periodic Benefit Cost - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Post Retirement Health Care And Life Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 13	$ 16	$ 26	$ 44
Interest cost	35	35	70	81
Expected return on assets	0	(84)	0	(239)
Amortization of net actuarial loss	69	5	139	5
Amortization of prior service cost	(84)	(52)	(169)	(52)
Total post-retirement benefit cost / (income)	33	(80)	66	(161)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	27	22	36	44
Expected return on assets	(34)	(26)	(45)	(52)
Amortization of net actuarial loss	20	5	25	10
Loss incurred in current year	(35)	0	(35)	0
Settlement costs	414	0	414	0
Total post-retirement benefit cost / (income)	$ 392	$ 1	$ 395	$ 2