Amounts Charged to Expense for Stock-based Compensation (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	$ 12,121		$ 3,914		$ 7,852
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	11,507		3,369		7,380
Directors restricted stock grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	420	[1]	413	[1]	390	[1]
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	$ 194		$ 132		$ 82

[1] Relates to non-employee directors serving on the Parent Company's Board of Directors, all of whom have been elected by the Company's stockholders, as well as non-employee directors serving on NUAL's Board of Directors.