Amounts Charged to Expense for Stock-based Compensation (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	$ 7,852		$ 460		$ 5,905
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	7,380	[1]	139	[1]	5,551	[1]
Directors restricted stock grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	390	[2]	248	[2]	210	[2]
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	82		173		221
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation			$ (100)	[3]	$ (77)	[3]

[1] The increase in RSU expense for 2012 as compared to 2011 is largely impacted by a $6.2 million reversal of RSU expense recorded in 2011 related to performance based awards that are not expected to vest, and to a lesser extent, the issuance of additional performance and non-performance RSU granted in 2012, partially offset by the impact of cancellations. The decrease in RSU expense for 2011 as compared to 2010 was primarily due to the reduction in RSU expense related to performance based awards not expected to vest.

[2] 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.

[3] All outstanding stock appreciation rights were exercised during 2011. The Company has no current plans to issue stock appreciation rights under the 2005 Amended and Restated Stock Incentive Plan.