Recent and Pending Accounting Standards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 191,796	$ 217,275
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized contract cost, amortization period	36 months
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized contract cost, amortization period	60 months
Accounting Standards Update 2014-09 | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 4,000
Deferred revenue	4,000
Prepaid commissions	0
Accounting Standards Update 2014-09 | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	7,000
Deferred revenue	6,000
Prepaid commissions	$ 3,000