Employee and Non-Employee Benefit Plans - Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Post Retirement Health Care And Life Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 13	$ 14	$ 39	$ 58
Interest cost	35	34	105	116
Loss incurred in current year	0	0	0	(52)
Amortization of net actuarial loss	70	7	209	12
Amortization of prior service cost	(85)	(66)	(254)	(305)
Total post-retirement benefit cost / (income)	33	(11)	99	(171)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0	22	36	66
Loss incurred in current year	0	0	(35)	0
Expected return on plan assets	0	(26)	(45)	(78)
Amortization of net actuarial loss	0	5	25	15
Settlement costs	0	0	(414)	0
Total post-retirement benefit cost / (income)	$ 0	$ 1	$ 395	$ 3