Stock-Based Compensation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-based compensation
Maximum number of awards that may be received by an individual in any one calendar year (in shares)	100,000
Number of shares of common stock remaining available for future grants of stock options, restricted stock or other forms of stock-based compensation under the 2001 Plan	87,202
Stock-based compensation expense	$ 1,102	$ 934	$ 1,082
Cost of revenues
Stock-based compensation
Stock-based compensation expense	185	174	188
Selling, general and administrative expense.
Stock-based compensation
Stock-based compensation expense	917	760	894
Maximum
Stock-based compensation
Number of shares of common stock that may be subject to outstanding awards granted under the 2001 Plan	650,000
Options
Stock-based compensation
Expiration period	10 years
Stock Options
Outstanding at the beginning of the period (in shares)	54,800
Granted (in shares)	9,900
Exercised (in shares)	(17,000)
Outstanding at the end of the period (in shares)	47,700	54,800
Exercisable at the end of the period (in shares)	47,700
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 42.58
Granted (in dollars per share)	$ 68.36
Exercised (in dollars per share)	$ 32.50
Outstanding at the end of the period (in dollars per share)	$ 51.52	$ 42.58
Exercisable at the end of the period (in dollars per share)	$ 51.52
Aggregate Intrinsic Value
Outstanding at the beginning of the period	1,019
Granted	45
Exercised	(657)	(263)	(559)
Outstanding at the end of the period	1,018	1,019
Exercisable at the end of the period	1,018
Additional disclosures
Weighted-average fair value of stock options granted during the year (in dollars per share)	$ 14.62	$ 12.47	$ 9.51
Weighted-average remaining contractual life for stock options	6 years 5 months 16 days	6 years 15 days	6 years 2 months 16 days
Total fair value of stock options vested during the year	145	123	94
Total intrinsic value of stock options exercised during the year	657	263	559
Weighted-average remaining contractual life of the outstanding and exercisable stock options	6 years 5 months 16 days
Non-vested stock options	0
Weighted-average assumptions used to estimate the fair value for the stock options
Dividend yield (as a percent)		0.00%	0.00%
Expected life	3 years
Options | Minimum
Weighted-average assumptions used to estimate the fair value for the stock options
Risk-free interest rates (as a percent)	0.89%	0.34%	0.36%
Dividend yield (as a percent)	0.70%
Volatility factor (as a percent)	0.294%	0.304%	0.278%
Options | Maximum
Weighted-average assumptions used to estimate the fair value for the stock options
Risk-free interest rates (as a percent)	1.17%	0.77%	0.51%
Dividend yield (as a percent)	0.90%
Volatility factor (as a percent)	0.316%	0.307%	0.288%
Options | Weighted-average
Weighted-average assumptions used to estimate the fair value for the stock options
Risk-free interest rates (as a percent)	1.10%	0.65%	0.40%
Dividend yield (as a percent)	0.75%
Volatility factor (as a percent)	0.299%	0.306%	0.286%
Restricted stock
Restricted Stock
Non-vested at the beginning of the period (in shares)	20,280
Granted (in shares)	16,015
Vested (in shares)	(16,227)
Forfeited (in shares)	(373)
Non-vested at the end of the period (in shares)	19,695	20,280
Weighted-Average Grant-Date Fair Value
Non-vested at the beginning of the period (in dollars per share)	$ 51.69
Granted (in dollars per share)	$ 65.81
Vested (in dollars per share)	$ 58.81
Forfeited (in dollars per share)	$ 54.10
Non-vested at the end of the period (in dollars per share)	$ 54.69	$ 51.69
Additional disclosures
Total fair value of restricted stock vested during the year	955	811	988
Total compensation cost not yet recognized	$ 929
Weighted-average period for recognition of total compensation cost not yet recognized	1 year 29 days
Restricted stock | Minimum
Stock-based compensation
Vesting period	6 months
Restricted stock | Maximum
Stock-based compensation
Vesting period	3 years