Schedule of Changes in SARs (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 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 June 30,	270,309	347,285
Vested and expected to vest at June 30,			263,546	339,980
Exercisable at June 30,			162,895	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 June 30,	$ 41.86	$ 38.94
Vested and expected to vest at June 30,			$ 41.70	$ 38.88
Exercisable at June 30,			$ 38.31	$ 35.68
Weighted-Average Remaining Contractual Term (in years)
Outstanding at June 30,	7 years 5 months 9 days	7 years 9 months 18 days
Vested and expected to vest at June 30,	7 years 4 months 23 days	7 years 8 months 12 days
Exercisable at June 30,	6 years 5 months	6 years 10 months 24 days
Share based compesation aggregate intrinsic value
Outstanding beginning of year, January 1,	$ 4,258	$ 5,107	$ 4,258	$ 5,107
Outstanding at June 30,	$ 4,258	$ 5,107
Vested and expected to vest at June 30,			4,193	5,019
Exercisable at June 30,			3,144	$ 3,433
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized			$ 2,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	2 years 27 days
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised	(114,853)	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 38.71	$ 0.00
Share based exercised awards intrinsic value	$ 2,488