Fair Value of Stock Settled Performance Units (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Performance Unit Awards 2014
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Performance Options [Line Items]
Fair value at date of grant	$ 5,388
Performance Unit Awards 2013
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Performance Options [Line Items]
Fair value at date of grant	5,564
Performance Unit Awards 2012
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Performance Options [Line Items]
Fair value at date of grant	3,065
Performance Unit Awards 2011
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Performance Options [Line Items]
Fair value at date of grant	$ 5,569