Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011	Mar. 30, 2012	Mar. 31, 2012 Employee Stock Purchase Plan	Mar. 31, 2011 Employee Stock Purchase Plan	Mar. 31, 2012 Employee Stock Purchase Plan	Mar. 31, 2011 Employee Stock Purchase Plan	Mar. 31, 2012 Restricted stock	Mar. 31, 2011 Restricted stock	Mar. 31, 2012 Restricted stock Year	Mar. 31, 2011 Restricted stock	Mar. 31, 2012 Restricted stock Senior Management	Dec. 31, 2011 Restricted stock Senior Management	Mar. 31, 2012 Restricted stock Senior Management Maximum	Mar. 31, 2012 Restricted stock Senior Management Awards subject to performance criteria	Dec. 31, 2011 Restricted stock Senior Management Awards subject to performance criteria	Mar. 31, 2012 Restricted stock Senior Management Awards subject to service criteria	Dec. 31, 2011 Restricted stock Senior Management Awards subject to service criteria	Dec. 31, 2011 Restricted stock Chief Executive Officer Phantom Stock Units	Mar. 31, 2012 Restricted stock Chief Executive Officer Phantom Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stocks granted												1,844,482		150,000	1,377,000		112,500	1,007,750	37,500	369,250	100,000
Total compensation expense on awards																$ 19,400,000
Restricted stocks granted, financial performance measurement year																	2014
Liability related to potential cash payment																						83,000
Closing stock price					$ 12.33
Cash received from participants stock option exercises	103,000	6,000	103,000	6,000
Total intrinsic value of options exercised	56,000	15,000	56,000	15,000
Fair value of restricted stock awards vested										3,200,000	2,000,000	3,600,000	6,300,000
Unrecognized compensation cost										15,700,000		15,700,000
Unrecognized compensation cost, estimated weighted average amortization period												2.1
Stock purchase under employee stock purchase plan						90,433	103,684	90,433	103,684
Proceeds from issuance of shares under ESPP						$ 700,000	$ 700,000	$ 700,000	$ 700,000