Employee Benefit Plans, Changes in Benefit Obligation and Plan Assets (Details) - Defined Benefit Pension Plans Combined [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Benefit Plans [Abstract]
Maximum period of eligible service		30 years
Change in discount rate		0.40%	(0.85%)
Threshold for amortization of gains and losses		10.00%
Estimated employer contributions		$ 2,300
Change in Benefit Obligation [Abstract]
Pension benefit obligation beginning of year		40,884	$ 32,054
Service cost		1,166	952	$ 1,188
Interest cost		1,515	1,444	1,280
Actuarial (gain) loss		(2,873)	7,762
Plan amendments		0	(210)
Benefit payments		(1,223)	(1,118)
Pension benefit obligation end of year		39,469	40,884	32,054
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year		30,575	27,102
Actual return on plan assets		183	2,409
Employer contributions		2,300	2,182
Benefits paid		(1,223)	(1,118)
Fair value of plan assets end of year		31,835	30,575	27,102
Funded Status of Plans at End of Year		(7,634)	(10,309)
Changes in Plan Assets and Benefit Obligations Recognized in Regulatory Assets [Abstract]
Net (gain) loss arising during the period		(826)	7,339
Recognized net actuarial loss		(705)	(126)	(698)
Recognized prior service credit (cost)		13	(197)
Total changes in regulatory asset during the year		(1,518)	7,016
Amounts Recognized in Regulatory Assets that Have Not Yet Been Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss		10,447	11,978
Prior service (credit) cost		(127)	(140)
Regulatory asset		10,320	11,838
Components of Net Periodic Benefit Cost [Abstract]
Service cost		1,166	952	1,188
Interest cost		1,515	1,444	1,280
Expected return on plan assets		(2,229)	(1,986)	(1,644)
Amortization of loss		705	126	698
Amortization of prior service (credit) cost		(13)	(13)	10
Rate-regulated adjustment		1,156	1,659	61
Net periodic benefit cost		2,300	2,182	$ 1,593
Change in defined benefit plan regulatory asset from pension contribution greater (less) than net periodic benefit cost		1,156
Cash and Money Market Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[1]	1,064
Fair value of plan assets end of year	[1]	1,205	1,064
Common Equity Securities [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[2]	3,031
Fair value of plan assets end of year	[2]	2,686	3,031
Equity Mutual Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[3]	16,380
Fair value of plan assets end of year	[3]	18,017	16,380
U.S. Treasury Obligations [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year		831
Fair value of plan assets end of year		833	831
Corporate and Foreign Bonds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[4]	1,620
Fair value of plan assets end of year	[4]	3,427	1,620
Fixed Income Mutual Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[5]	7,649
Fair value of plan assets end of year	[5]	5,667	7,649
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year		28,124
Fair value of plan assets end of year		27,575	28,124
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Money Market Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[1]	1,064
Fair value of plan assets end of year	[1]	1,205	1,064
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Common Equity Securities [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[2]	3,031
Fair value of plan assets end of year	[2]	2,686	3,031
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[3]	16,380
Fair value of plan assets end of year	[3]	18,017	16,380
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury Obligations [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year		0
Fair value of plan assets end of year		0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate and Foreign Bonds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[4]	0
Fair value of plan assets end of year	[4]	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fixed Income Mutual Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[5]	7,649
Fair value of plan assets end of year	[5]	5,667	7,649
Significant Other Observable Inputs (Level 2) [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year		2,451
Fair value of plan assets end of year		4,260	2,451
Significant Other Observable Inputs (Level 2) [Member] | Cash and Money Market Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[1]	0
Fair value of plan assets end of year	[1]	0	0
Significant Other Observable Inputs (Level 2) [Member] | Common Equity Securities [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[2]	0
Fair value of plan assets end of year	[2]	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[3]	0
Fair value of plan assets end of year	[3]	0	0
Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury Obligations [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year		831
Fair value of plan assets end of year		833	831
Significant Other Observable Inputs (Level 2) [Member] | Corporate and Foreign Bonds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[4]	1,620
Fair value of plan assets end of year	[4]	3,427	1,620
Significant Other Observable Inputs (Level 2) [Member] | Fixed Income Mutual Funds [Member]
Change in Plan Assets [Abstract]
Fair value of plan assets beginning of year	[5]	0
Fair value of plan assets end of year	[5]	$ 0	$ 0

[1] The portfolios are designed to keep approximately three months of distributions in immediately available funds. The Company was more heavily-weighted in cash as of December 31, 2015 due to market volatility.

[2] This category includes investments in U.S. common stocks and foreign stocks trading in the U.S. widely distributed among consumer discretionary, consumer staples, healthcare, information technology, financial services, materials, industrials and energy. The individual stocks are primarily large cap stocks which track with the S&P 500 with the exception of $447 in 2014 which was invested in York Water Company common stock. In 2015, the Company repurchased the company stock previously held in the pension portfolio.

[3] This category currently includes a majority of investments in closed-end mutual funds as well as domestic equity mutual funds and international mutual funds which give the portfolio exposure to mid and large cap index funds as well as international diversified index funds.

[4] This category currently includes only U.S. corporate bonds and notes widely distributed among consumer discretionary, consumer staples, healthcare, information technology and financial services.

[5] This category includes fixed income investments in mutual funds which include government, corporate and mortgage securities of both the U.S. and other countries. The mortgage-backed securities and non-U.S. corporate and sovereign investments add further diversity to the fixed income portion of the portfolio.