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Stock-Based Compensation Expense in Future for Outstanding Awards (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
2015 $ 8,407mlm_FutureShareBasedCompensationExpenseYearOne
2016 6,182mlm_FutureShareBasedCompensationExpenseYearTwo
2017 3,482mlm_FutureShareBasedCompensationExpenseYearThree
2018 2,743mlm_FutureShareBasedCompensationExpenseYearFour
2019 1,764mlm_FutureShareBasedCompensationExpenseYearFive
Total $ 22,578mlm_FutureShareBasedCompensationExpense