Fair Value Measurements - Marketable Securities and Deferred Compensation Fund Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial Assets:
Marketable securities	$ 67,730	$ 69,496
Deferred compensation fund	24,119	25,391
Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	20,972	21,495
Significant Other Observable Inputs (Level 2)
Financial Assets:
Deferred compensation fund	3,147	3,896
Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
Carrying Amount
Financial Assets:
Deferred compensation fund	24,119	25,391
Total Fair Value
Financial Assets:
Deferred compensation fund	24,119	25,391
Marketable securities | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Marketable securities	0	0
Marketable securities | Significant Other Observable Inputs (Level 2)
Financial Assets:
Marketable securities	67,730	69,496
Marketable securities | Significant Unobservable Inputs (Level 3)
Financial Assets:
Marketable securities	0	0
Marketable securities | Carrying Amount
Financial Assets:
Marketable securities	67,730	69,496
Marketable securities | Total Fair Value
Financial Assets:
Marketable securities	67,730	69,496
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	3,147	3,896
Money Market | Significant Unobservable Inputs (Level 3)
Financial Assets:
Deferred compensation fund	0	0
Money Market | Carrying Amount
Financial Assets:
Deferred compensation fund	3,147	3,896
Money Market | Total Fair Value
Financial Assets:
Deferred compensation fund	3,147	3,896
Balanced and Lifestyle | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	7,162	9,136
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	7,162	9,136
Balanced and Lifestyle | Total Fair Value
Financial Assets:
Deferred compensation fund	7,162	9,136
Large Cap Growth | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	5,583	5,218
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	5,583	5,218
Large Cap Growth | Total Fair Value
Financial Assets:
Deferred compensation fund	5,583	5,218
Small Cap Value | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund		2,275
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		2,275
Small Cap Value | Total Fair Value
Financial Assets:
Deferred compensation fund		2,275
Small Cap Growth | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	2,933
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	2,933
Small Cap Growth | Total Fair Value
Financial Assets:
Deferred compensation fund	2,933
Fixed Income | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	2,752	2,624
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	2,752	2,624
Fixed Income | Total Fair Value
Financial Assets:
Deferred compensation fund	2,752	2,624
International | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	1,132	1,025
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	1,132	1,025
International | Total Fair Value
Financial Assets:
Deferred compensation fund	1,132	1,025
Mid Cap Growth | Quoted Prices in Active Markets (Level 1)
Financial Assets:
Deferred compensation fund	1,410	1,217
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	1,410	1,217
Mid Cap Growth | Total Fair Value
Financial Assets:
Deferred compensation fund	$ 1,410	$ 1,217