Revenue Recognition - Impact on Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets	$ 27,687	$ 30,683
Accrued income taxes	8,974	11,503
Deferred revenue and customer deposits	13,252	9,420
Retained earnings	$ 670,935	668,587
As previously reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets		30,800
Accrued income taxes		11,391
Deferred revenue and customer deposits		9,969
Retained earnings		668,267
Adjustment | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets		(117)
Accrued income taxes		112
Deferred revenue and customer deposits		(549)
Retained earnings		$ 320