Stock-Based Compensation Narrative (Detail) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended			4 Months Ended	3 Months Ended					4 Months Ended	3 Months Ended				4 Months Ended	3 Months Ended		4 Months Ended	6 Months Ended			3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Mar. 28, 2013	Mar. 31, 2013 Restricted Stock	Mar. 31, 2012 Restricted Stock	Mar. 31, 2013 Restricted Stock	Mar. 31, 2012 Restricted Stock	Mar. 31, 2013 Restricted Stock Senior Management	Dec. 31, 2012 Restricted Stock Senior Management	Mar. 31, 2012 Restricted Stock Senior Management	Dec. 31, 2011 Restricted Stock Senior Management	Mar. 31, 2013 Restricted Stock Senior Management Maximum	Sep. 30, 2011 Restricted Stock Senior Management Maximum	Mar. 31, 2013 Restricted Stock Senior Management Awards Subject to Service Criteria	Dec. 31, 2012 Restricted Stock Senior Management Awards Subject to Service 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	Mar. 31, 2013 Restricted Stock Senior Management Awards Subject to Performance Criteria	Dec. 31, 2012 Restricted Stock Senior Management Awards Subject to Performance Criteria	Mar. 31, 2012 Restricted Stock Senior Management Awards Subject to Performance Criteria	Sep. 30, 2011 Restricted Stock Senior Management Awards Subject to Performance Criteria	Dec. 31, 2011 Restricted Stock Senior Management Awards Subject to Performance Criteria	Mar. 31, 2013 Restricted Stock Chief Executive Officer Phantom Stock Units	Mar. 31, 2012 Restricted Stock Chief Executive Officer Phantom Stock Units	Dec. 31, 2011 Restricted Stock Chief Executive Officer Phantom Stock Units	Mar. 31, 2013 Restricted Stock Chief Executive Officer Phantom Stock Units	Mar. 31, 2012 Restricted Stock Chief Executive Officer Phantom Stock Units	Sep. 30, 2012 Restricted Stock Chief Executive Officer Phantom Stock Units	Mar. 31, 2013 Employee Stock Purchase Plan	Mar. 31, 2012 Employee Stock Purchase Plan	Mar. 31, 2013 Employee Stock Purchase Plan	Mar. 31, 2012 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stocks granted								1,297,439		40,500	1,183,500	150,000	1,377,000			22,375	524,250	37,500	369,250	18,125	659,250	112,500		1,007,750			100,000
Restricted stocks granted, financial performance measurement year																				2013			2014
Total compensation expense on awards	$ 2,499,000	$ 3,181,000	$ 5,010,000	$ 4,924,000		$ 2,382,000	$ 3,030,000	$ 4,766,000	$ 4,625,000					$ 13,700,000	$ 15,600,000																$ 117,000	$ 151,000	$ 244,000	$ 299,000
Liability related to potential cash payment																									155,000			155,000		78,000
Cash settlement of phantom unit award																									32,000	58,000		77,000	83,000
Closing stock price					$ 10.18
Total intrinsic value of options exercised	19,000	56,000	19,000	56,000
Proceeds from stock options exercised	67,000	103,000	67,000	103,000
Fair value of restricted stock awards vested						3,100,000	3,200,000	6,000,000	3,600,000
Unrecognized compensation cost						10,400,000		10,400,000
Unrecognized compensation cost, estimated weighted average amortization period						1 year 9 months
Stock purchase under employee stock purchase plan																															115,751	90,433	115,751	90,433
Proceeds from issuance of shares under ESPP																															$ 900,000	$ 700,000	$ 900,000	$ 700,000