Summary of Performance Stock 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
Performance Stock Plan
Weighted-Average Grant Date Fair Value
Weighted-Average Grant Date Fair Value, Outstanding beginning balance	$ 8.08	$ 7.32	$ 7.39
Weighted-Average Grant Date Fair Value, Granted	$ 0.00	$ 0.00	$ 9.67
Weighted-Average Grant Date Fair Value, Awarded	$ 8.09	$ 9.56	$ 9.49
Weighted-Average Grant Date Fair Value, Vested	$ 3.29	$ 6.01	$ 2.02
Weighted-Average Grant Date Fair Value, Forfeited	$ 13.06	$ 9.48	$ 7.91
Weighted-Average Grant Date Fair Value, Outstanding ending balance	$ 8.72	$ 8.08	$ 7.32
Granted Shares
Granted Shares, Outstanding beginning balance	4,931,812	5,791,854	7,758,547
Granted Shares, Granted			384,420
Granted Shares, Awarded
Granted Shares, Vested	(877,224)	(106,490)	(1,388,789)
Granted Shares, Forfeited	(363,566)	(753,552)	(962,324)
Granted Shares, Outstanding ending balance	3,691,022	4,931,812	5,791,854
Awarded Shares
Awarded Shares, Outstanding beginning balance	3,345,269	3,391,519	4,423,436
Awarded Shares, Granted
Awarded Shares, Awarded	7,743	447,154	474,113
Awarded Shares, Vested	(877,224)	(106,490)	(1,388,789)
Awarded Shares, Forfeited	(81,283)	(386,914)	(117,241)
Awarded Shares, Outstanding ending balance	2,394,505	3,345,269	3,391,519
Shares Not Yet Awarded
Shares Not Yet Awarded, Outstanding beginning balance	1,586,543	2,400,335	3,335,111
Shares Not Yet Awarded, Granted			384,420
Shares Not Yet Awarded, Awarded	(7,743)	(447,154)	(474,113)
Shares Not Yet Awarded, Forfeited	(282,283)	(366,638)	(845,083)
Shares Not Yet Awarded, Outstanding ending balance	1,296,517	1,586,543	2,400,335