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Difference Between Statutory Federal Income Tax Rate and Effective Income Rate (Detail)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Tax Disclosure [Abstract]      
Statutory tax rate 35.00% 35.00% 35.00%
State income taxes 2.00% 2.10% 2.50%
Permanent differences (0.10%) (1.30%) (1.40%)
Other differences, net (1.10%) (2.40%) (0.10%)
Effective tax rate 35.80% 33.40% 36.00%