Related party transactions with affiliated company - Additional Information (Detail) (USD $)	3 Months Ended			3 Months Ended		3 Months Ended										3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Mar. 31, 2012 Prlp2011 Holdings Llc Joint Venture [Member]	Sep. 30, 2011 Prlp2011 Holdings Llc Joint Venture [Member]	Sep. 30, 2011 E V E R T E C Inc [Member]	Mar. 31, 2012 E V E R T E C Inc [Member]	Dec. 31, 2011 E V E R T E C Inc [Member]	Mar. 31, 2011 E V E R T E C Inc [Member]	Mar. 31, 2012 Performance Guarantee [Member] E V E R T E C Inc [Member]	Dec. 31, 2011 Performance Guarantee [Member] E V E R T E C Inc [Member]	Mar. 31, 2011 Performance Guarantee [Member] E V E R T E C Inc [Member]	Mar. 31, 2012 Financial Standby Letter Of Credit Member	Dec. 31, 2011 Financial Standby Letter Of Credit Member	Mar. 31, 2011 Financial Standby Letter Of Credit Member	Sep. 30, 2011 Financial Standby Letter Of Credit Member E V E R T E C Inc [Member]	Mar. 31, 2012 Financial Standby Letter Of Credit Member E V E R T E C Inc [Member]	Dec. 31, 2011 Financial Standby Letter Of Credit Member E V E R T E C Inc [Member]	Mar. 31, 2011 Financial Standby Letter Of Credit Member E V E R T E C Inc [Member]
Related Party Transaction [Line Items]
Sale of majority interest in subsidiaries, date of sale						Sep. 30, 2010
Percentage Of Ownership Interests Sold							51.00%
Equity Method Investments	$ 335,762,000	$ 294,559,000	$ 313,152,000				$ 192,000,000	$ 203,000,000	$ 203,000,000
Equity Method Investment Ownership Percentage				24.90%	24.90%		49.00%
Guarantee Obligations Current Carrying Value										14,000,000	15,000,000	10,400,000	1,000,000	500,000	600,000		2,900,000	2,900,000	2,900,000
Guarantee Obligations Term																5-year period
Financing Receivable Allowance For Credit Losses Write Offs	$ (144,689,000)	$ (171,101,000)
Majority Interest Percentage				75.00%