Summary Of Stock Incentive Plan Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Awarded Shares
Awarded Shares, Vested
Awarded Shares, Forfeited
Awarded Shares, Outstanding ending balance	37,408
Stock Incentive Plan
Weighted-Average Grant Date Fair Value
Weighted-Average Grant Date Fair Value, Outstanding beginning balance	$ 23.06	$ 12.62
Weighted-Average Grant Date Fair Value, Granted	$ 22.59	$ 23.94	$ 12.62
Weighted-Average Grant Date Fair Value, Awarded		$ 11.41	$ 12.62
Weighted-Average Grant Date Fair Value, Vested
Weighted-Average Grant Date Fair Value, Forfeited	$ 23.62	$ 23.94
Weighted-Average Grant Date Fair Value, Outstanding ending balance	$ 22.91	$ 23.06	$ 12.62
Granted Shares
Granted Shares, Outstanding beginning balance	2,478,057	192,245
Granted Shares, Granted	814,545	2,375,892	192,245
Granted Shares, Awarded
Granted Shares, Vested
Granted Shares, Forfeited	(135,291)	(90,080)
Granted Shares, Outstanding ending balance	3,157,311	2,478,057	192,245
Awarded Shares
Awarded Shares, Outstanding beginning balance	37,408	38,449
Awarded Shares, Granted
Awarded Shares, Awarded		1,041	38,449
Awarded Shares, Vested
Awarded Shares, Forfeited
Awarded Shares, Outstanding ending balance	37,408	37,408	38,449
Shares Not Yet Awarded
Shares Not Yet Awarded, Outstanding beginning balance	2,440,649	153,796
Shares Not Yet Awarded, Granted	814,545	2,375,892	192,245
Shares Not Yet Awarded, Awarded		1,041	38,449
Shares Not Yet Awarded, Forfeited	(135,291)	(90,080)
Shares Not Yet Awarded, Outstanding ending balance	3,119,903	2,440,649	153,796