Line of Credit - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2015	Jun. 30, 2015
Senior Unsecured Revolving Line of Credit [Member]
Line of Credit Facility [Line Items]
Senior unsecured revolving line of credit aggregate commitment			$ 100.0
Sublimit for letters of credit			25.0
Line of credit facility expansion feature			50.0
Replacement Facility [Member]
Line of Credit Facility [Line Items]
Long-term debt, gross			$ 26.5
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Long-term debt, gross		$ 26.5
Term Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum amount outstanding during period	$ 29.5