Non-Vested Stock Award Activity (Detail) (Non-Vested Stock, USD $)	12 Months Ended
	Dec. 31, 2012
Non-Vested Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Non-vested Beginning Balance	568,850
Shares, Granted	401,249
Shares, Vested	(253,862)
Shares, Canceled, forfeited or expired	(72,884)
Shares, Non-vested Ending Balance	643,353
Weighted average grant date fair Value, Non-vested Beginning Balance	$ 32.64
Weighted average grant date fair Value, Granted	$ 14.01
Weighted average grant date fair Value, Vested	$ 33.63
Weighted average grant date fair Value, Canceled, forfeited or expired	$ 28.92
Weighted average grant date fair Value, Non-vested Ending Balance	$ 20.76