Stockholders' Equity - Summary of Information Regarding Stock Option Exercises (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Cash received from issuance of common stock	$ 98	$ 118	$ 182
Intrinsic value of stock options exercised	194	290	1,057
Tax benefit from exercises	$ 60	$ 94	$ 54