Amounts Charged to Expense for Stock-based Compensation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	$ 2,584		$ 2,260		$ 4,643		$ 3,727
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	2,484		2,116		4,369		3,474
Directors restricted stock grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	100	[1]	106	[1]	200	[1]	206	[1]
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation			$ 38		$ 74		$ 47

[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.