Stockholders' Equity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Nov. 30, 2018	Dec. 31, 2017
Stockholders' equity
Common stock, outstanding shares (in shares)	16,866,000		16,859,000
Cost of shares of common stock acquired	$ 300,000	$ 5,300,000
Stock acquired (in shares)	923
Maximum
Stockholders' equity
Stock acquired	$ 100,000
2019 Stock Purchase Plan
Stockholders' equity
Common stock purchased under the stock purchase plan (in shares)	4,285	0
Cost of shares of common stock acquired	$ 300,000	$ 0
2019 Stock Purchase Plan | Maximum
Stockholders' equity
Authorized amount of repurchase under the stock purchase plan (up to)				$ 25,000,000
2018 Stock Purchase Plan
Stockholders' equity
Common stock purchased under the stock purchase plan (in shares)	0	66,724
Cost of shares of common stock acquired	$ 0	$ 5,300,000
2018 Stock Purchase Plan | Maximum
Stockholders' equity
Authorized amount of repurchase under the stock purchase plan (up to)			$ 25,000,000
2017 Stock Purchase Plan | Maximum
Stockholders' equity
Authorized amount of repurchase under the stock purchase plan (up to)					$ 25,000,000