Activity of Awarded Restricted Stock Units (Detail) (USD $)	12 Months Ended					12 Months Ended
	Dec. 31, 2013 Restricted Stock Units (RSUs)		Dec. 31, 2013 Performance Based Restricted Stock Units (PBRSUs)	Dec. 31, 2013 Retirement Eligible Employees, Equity Award Restricted Stock Units (RSUs)	Dec. 31, 2012 Retirement Eligible Employees, Equity Award Restricted Stock Units (RSUs)	Dec. 31, 2013 Minimum Performance Based Restricted Stock Units (PBRSUs)	Dec. 31, 2013 Maximum Performance Based Restricted Stock Units (PBRSUs)
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Shares, Expected to Vest, Percentage						0.00%	200.00%
Number of shares
Balance at beginning of year (in shares)	91,971	[1]	200,824	346,777.000	78,864.000
Granted (in shares)	754,474		360,486
Vested (in shares)	(345,595)
Forfeited (in shares)	0		0
Balance at end of year (in shares)	500,850	[1]	561,310	346,777.000	78,864.000
Weighted-Average Grant Date Fair Value
Balance at beginning of year (in dollars per share)	$ 10.08	[1]	$ 6.67
Granted (in dollars per share)	$ 3.91		$ 4.91
Vested (in dollars per share)	$ 4.81
Forfeited (in dollars per share)	$ 0.00		$ 0.00
Balance at end of year (in dollars per share)	$ 4.42	[1]	$ 16.07

[1] Excludes 78,864 units at the beginning of the year and 346,777 units at the end of year that have vested due to retirement eligibility, but have not yet been settled or converted to common shares.