Long-Term Indebtedness (Details) (Line of Credit, USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Feb. 24, 2014	Dec. 31, 2013
Line of Credit Facility
Amount outstanding	15,700,000	$ 15,700,000		$ 0
Maximum borrowings under line of credit			50,000,000.0
Remaining availability under the facilities	207,400,000	207,400,000
Maximum leverage ratio	2.5	2.5
Maximum
Line of Credit Facility
Weighted average interest rate	1.90%
JPMorgan Chase Bank And Wells Fargo Bank
Line of Credit Facility
Maximum borrowings under line of credit	75,000,000.0	75,000,000.0	75,000,000.0
Potential increase in line of credit borrowing capacity			25,000,000.0
Letter of credit	1,900,000	1,900,000		2,200,000
Remaining availability under the facilities	57,400,000	57,400,000
Expected maximum borrowing capacity	100,000,000.0	100,000,000.0
Expected term extension		1 year
Expected maximum borrowing capacity, if extension is granted	125,000,000	125,000,000
JPMorgan Chase Bank And Wells Fargo Bank | Prime Rate
Line of Credit Facility
Interest rate		1.00%
Stated interest rate		1.50%
JPMorgan Chase Bank And Wells Fargo Bank | Prime Rate | Minimum
Line of Credit Facility
Interest rate		0.75%
JPMorgan Chase Bank And Wells Fargo Bank | Prime Rate | Maximum
Line of Credit Facility
Interest rate		1.00%
JPMorgan Chase Bank And Wells Fargo Bank | LIBOR Plus
Line of Credit Facility
Interest rate		1.75%
JPMorgan Chase Bank And Wells Fargo Bank | LIBOR Plus | Minimum
Line of Credit Facility
Interest rate		1.75%
JPMorgan Chase Bank And Wells Fargo Bank | LIBOR Plus | Maximum
Line of Credit Facility
Interest rate		2.00%
Prudential Investment Management Inc
Line of Credit Facility
Amount outstanding	0	0		0
Remaining availability under the facilities	150,000,000.0	$ 150,000,000.0
Period after request is issued, by company, for interest payable rate to be determined by Prudential		5 days
Prudential Investment Management Inc | Maximum
Line of Credit Facility
Maturity period of Promissory Notes		12 years