Activity of Awarded Deferred Common Stock Units (Detail) - Deferred Common Stock Units	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Number of shares
Balance at beginning of year (in shares) | shares	253,879
Granted (in shares) | shares	195,395
Converted (in shares) | shares	(1,776)
Balance at end of year (in shares) | shares	447,498
Weighted-Average Grant Date Fair Value
Balance at beginning of year (in dollars per share) | $ / shares	$ 12.81
Granted (in dollars per share) | $ / shares	1.33
Converted (in dollars per share) | $ / shares	16.89
Balance at end of year (in dollars per share) | $ / shares	$ 7.75