Fair Value Measurements - Marketable Securities and Deferred Compensation Fund Investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets, Fair Value Disclosure [Abstract]
Marketable securities	$ 11,799	$ 11,445	$ 21,322
Deferred compensation fund	24,742	22,200
Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	20,464	18,608
Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	4,278	3,592
Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	24,742	22,200
Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	24,742	22,200
Municipal Bonds [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Marketable securities	0	0
Municipal Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Marketable securities	11,799	11,445
Municipal Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Marketable securities	0	0
Municipal Bonds [Member] | Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Marketable securities	11,799	11,445
Municipal Bonds [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Marketable securities	11,799	11,445
Money Market [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Money Market [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	4,278	3,592
Money Market [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Money Market [Member] | Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	4,278	3,592
Money Market [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	4,278	3,592
Balanced And Lifestyle [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	8,885	8,174
Balanced And Lifestyle [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Balanced And Lifestyle [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Balanced And Lifestyle [Member] | Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	8,885	8,174
Balanced And Lifestyle [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	8,885	8,174
Large Cap Growth [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	4,856	4,292
Large Cap Growth [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Large Cap Growth [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Large Cap Growth [Member] | Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	4,856	4,292
Large Cap Growth [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	4,856	4,292
Small Cap Value [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	2,392	2,173
Small Cap Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Small Cap Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Small Cap Value [Member] | Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	2,392	2,173
Small Cap Value [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	2,392	2,173
Fixed Income [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	2,081	1,962
Fixed Income [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Fixed Income [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Fixed Income [Member] | Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	2,081	1,962
Fixed Income [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	2,081	1,962
International [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	1,097	1,079
International [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
International [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
International [Member] | Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	1,097	1,079
International [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	1,097	1,079
Mid Cap Growth [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	1,153	928
Mid Cap Growth [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Mid Cap Growth [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	0	0
Mid Cap Growth [Member] | Carrying Amount [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	1,153	928
Mid Cap Growth [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Deferred compensation fund	$ 1,153	$ 928