Commitments and Contingencies (Narrative) (Detail) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) Officers $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Employee Separation Expenses [Line Items]
Unaccrued contractual and other commitments		$ 186,700
Number of officers | Officers		3
Aggregate base compensation		$ 1,600
Provision For Employee Separation Expenses		1,355	$ 2,087	$ 4,961
Employee Termination Expenses		1,400	$ 2,100	$ 900
Environmental insurance coverage claims per occurrence		25,000
Environmental insurance coverage claims aggregate		$ 25,000
Restricted Stock [Member]
Employee Separation Expenses [Line Items]
RSUs granted | shares		264,989	195,255	253,922
Grant date fair value (in dollars per share) | $ / shares		$ 19.27	$ 23.38	$ 19.20
Officer [Member]
Employee Separation Expenses [Line Items]
Renewal of agreements term		1 year
Officer [Member] | Minimum [Member]
Employee Separation Expenses [Line Items]
Initial year of employment agreement of employee		1 year
Officer [Member] | Maximum [Member]
Employee Separation Expenses [Line Items]
Initial year of employment agreement of employee		3 years
Mr Rubin [Member]
Employee Separation Expenses [Line Items]
Provision For Employee Separation Expenses			$ 4,100
Payments to Employees	$ 2,600
Credit Agreements [Member]
Employee Separation Expenses [Line Items]
Ratio of total liabilities to gross asset value		0.60
Credit Agreements [Member] | Minimum [Member]
Employee Separation Expenses [Line Items]
Ratio of total liabilities to gross asset value		0.60
Credit Agreements [Member] | Maximum [Member]
Employee Separation Expenses [Line Items]
Ratio of total liabilities to gross asset value		0.625