Compensation Expense Associated with Performance Units (Detail) - Performance Units Awards - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units	$ 321		$ 321
2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units	338	$ 338	675	$ 338
2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units	$ 449	449	898	898
2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units		$ 464	$ 464	928
2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units				$ 255