Schedule of Changes in SARs (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award	The SARs vest ratably over a three-year period and may be exercised at any point after vesting through ten years from the date of issuance. Pursuant to the terms of the awards, upon exercise, the executive officers will receive, in shares of common stock, the excess of the market price of the award on the date of exercise over the market price of the award on the date of issuance.
Stock Appreciation Rights (SARs)
Number of SARs
Outstanding beginning of year, January 1,	326,453	279,011
Awarded	58,709	68,274
Outstanding at March 31,	376,748	347,285
Vested and expected to vest at March 31,			368,662	338,570
Exercisable at March 31,			243,103	191,149
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price
Outstanding beginning of year, January 1,	$ 38.99	$ 38.77
Awarded	51.63	39.63
Outstanding at March 31,	$ 40.86	$ 38.94
Vested and expected to vest at March 31,			$ 40.71	$ 38.86
Exercisable at March 31,			$ 37.44	$ 35.68
Weighted-Average Remaining Contractual Term (in years)
Outstanding at March 31,	7 years 5 months 11 days	8 years
Vested and expected to vest at March 31,	7 years 4 months 23 days	8 years
Exercisable at March 31,	6 years 6 months 28 days	7 years 1 month
Share based compesation aggregate intrinsic value
Outstanding beginning of year, January 1,	$ 7,002	$ 5,245	$ 7,002	$ 5,245
Outstanding at March 31,	$ 7,002	$ 5,245
Vested and expected to vest at March 31,			6,909	5,138
Exercisable at March 31,			5,350	$ 3,509
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized			$ 2,700
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	2 years 10 days
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised	(8,414)	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 43.38	$ 0.00
Share based exercised awards intrinsic value	$ 114	$ 0