Share-Based Transactions - Summary of Intrinsic Value, Tax Benefit Realized and Value of Shares Withheld Related to Option Exercise Activity (Details) - Employee Stock Option [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Intrinsic value of options exercised	$ 1,453	$ 2,755	$ 1,620
Tax benefit realized from the options exercised	509	964	567
Value of issued shares withheld to satisfy option exercise price	$ 1,673	$ 5,509	$ 2,966