Deferred costs and other intangibles - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013
Goodwill And Intangible Assets Disclosure [Abstract]
Amortization expense	$ 3,202,000	$ 5,109,000
Amortization of deferred financing costs	$ 2,202,000	$ 3,054,000