Summary of Significant Accounting Policies - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Shares
Options outstanding at beginning of period (in shares)	2,250
Exercised (in Shares)	(2,250)
Options outstanding at end of period (in shares)		0	2,250
Exercisable at end of year (in shares)		24,000
Exercise Price
Options outstanding at beginning of year (in dollars per share)	$ 37.17
Exercised (in dollars per share)	$ 37.17
Options outstanding at end of year (in dollars per share)			$ 37.17
Exercisable at end of year		$ 38.39
Additional information
Remaining Contractual Life - Outstanding Options (in years)			3 months 18 days
Remaining Contractual Life - Exercisable Options - (in years)		7 months 6 days
Intrinsic value of unexercised in-the-money options - Outstanding Options (in dollars)			$ 29
Intrinsic value of unexercised in-the-money options - Exercisable Options (in dollars)		$ 12