Fair Value Measurements - Marketable Securities and Deferred Compensation Fund Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial Assets:
Marketable securities	$ 69,496	$ 11,799
Deferred compensation fund	25,391	24,742
Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	21,495	20,464
Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	3,896	4,278
Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
Carrying Amount
Financial Assets:
Deferred compensation fund	25,391	24,742
Total Fair Value
Financial Assets:
Deferred compensation fund	$ 25,391	24,742
Municipal bonds — available for sale | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Marketable securities		0
Municipal bonds — available for sale | Significant Other Observable Inputs (Level 2)
Financial Assets:
Marketable securities	$ 69,496	11,799
Municipal bonds — available for sale | Significant Unobservable Inputs (Level 3)
Financial Assets:
Marketable securities	0	0
Municipal bonds — available for sale | Carrying Amount
Financial Assets:
Marketable securities	69,496	11,799
Municipal bonds — available for sale | Total Fair Value
Financial Assets:
Marketable securities	69,496	11,799
Money Market | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	0	0
Money Market | Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	3,896	4,278
Money Market | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
Money Market | Carrying Amount
Financial Assets:
Deferred compensation fund	3,896	4,278
Money Market | Total Fair Value
Financial Assets:
Deferred compensation fund	3,896	4,278
Balanced and Lifestyle | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	9,136	8,885
Balanced and Lifestyle | Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	0	0
Balanced and Lifestyle | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
Balanced and Lifestyle | Carrying Amount
Financial Assets:
Deferred compensation fund	9,136	8,885
Balanced and Lifestyle | Total Fair Value
Financial Assets:
Deferred compensation fund	9,136	8,885
Large Cap Growth | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	5,218	4,856
Large Cap Growth | Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	0	0
Large Cap Growth | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
Large Cap Growth | Carrying Amount
Financial Assets:
Deferred compensation fund	5,218	4,856
Large Cap Growth | Total Fair Value
Financial Assets:
Deferred compensation fund	5,218	4,856
Small Cap Value | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund		2,392
Small Cap Value | Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund		0
Small Cap Value | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund		0
Small Cap Value | Carrying Amount
Financial Assets:
Deferred compensation fund		2,392
Small Cap Value | Total Fair Value
Financial Assets:
Deferred compensation fund		2,392
Small Cap Growth | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	2,275
Small Cap Growth | Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	0
Small Cap Growth | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0
Small Cap Growth | Carrying Amount
Financial Assets:
Deferred compensation fund	2,275
Small Cap Growth | Total Fair Value
Financial Assets:
Deferred compensation fund	2,275
Fixed Income | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	2,624	2,081
Fixed Income | Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	0	0
Fixed Income | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
Fixed Income | Carrying Amount
Financial Assets:
Deferred compensation fund	2,624	2,081
Fixed Income | Total Fair Value
Financial Assets:
Deferred compensation fund	2,624	2,081
International | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	1,025	1,097
International | Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	0	0
International | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
International | Carrying Amount
Financial Assets:
Deferred compensation fund	1,025	1,097
International | Total Fair Value
Financial Assets:
Deferred compensation fund	1,025	1,097
Mid Cap Growth | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	1,217	1,153
Mid Cap Growth | Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	0	0
Mid Cap Growth | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
Mid Cap Growth | Carrying Amount
Financial Assets:
Deferred compensation fund	1,217	1,153
Mid Cap Growth | Total Fair Value
Financial Assets:
Deferred compensation fund	$ 1,217	$ 1,153