Equity Offering - Additional Information (Detail) $ / shares in Units, shares in Millions, $ in Millions	Sep. 18, 2018 USD ($) $ / shares shares
Equity Offering [Abstract]
Number of shares of common stock sold (in shares) | shares	14.4
Public offering price per share | $ / shares	$ 16.00
Net proceeds to NN from the offering | $	$ 217.3