Debt - Additional Information (Detail) (USD $)	9 Months Ended			0 Months Ended	9 Months Ended	0 Months Ended				9 Months Ended	0 Months Ended		9 Months Ended	0 Months Ended
	Sep. 30, 2014	Jun. 18, 2014	Dec. 31, 2013	Jan. 07, 2014 Promissory note	Sep. 30, 2014 Promissory note	Jun. 18, 2014 Minimum	Jun. 18, 2014 Maximum	Jun. 18, 2014 Federal funds rate	Jun. 18, 2014 Eurodollar Instruments	Sep. 30, 2014 Eurodollar	Jun. 18, 2014 Eurodollar Minimum	Jun. 18, 2014 Eurodollar Maximum	Sep. 30, 2014 Base rate	Jun. 18, 2014 Base rate Minimum	Jun. 18, 2014 Base rate Maximum
Debt Instrument [Line Items]
Maximum principal borrowing amount		$ 225,000,000
Letter of credit, sub-limit amount		15,000,000
Credit facility scheduled to expire	Jun. 18, 2019
Line of credit facility interest rate								0.50%	1.00%	2.40%	1.75%	2.50%	4.50%	0.75%	1.50%
Line of credit facility, borrowing outstanding									15
Line of credit facility, description	(a) the Federal Funds Rate in effect on such day plus 0.5% (b) the Prime Rate in effect on such day and (c) the Eurodollar Rate for a one month interest period on such day plus 1.0%, plus a margin ranging from 0.75% to 1.5% per annum or Eurodollar rate plus a margin ranging from 1.75% to 2.5% per annum. Swing line loans bear interest at the Base Rate.
Commitment fee rates for unused commitments						0.225%	0.375%
Line of credit facility, interest rate at period end	2.40%
Line of credit facility drawn	64,000,000		22,000,000
Letter of credit outstanding	7,100,000		6,700,000
Available credit under agreement	153,900,000
Promissory note aggregate principal amount				1,200,000
Promissory note maturity date					Jan. 06, 2019
Promissory note principal payment				$ 20,000
Debt instrument, term				60 months
Promissory note interest rate percentage				4.50%