Stockholders' Equity and Equity Compensation Plans (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2014
Stockholders Equity And Equity Compensation Plans [Line Items]
Remaining number of shares available for repurchase	5,100,000		5,100,000
Repurchase of common stock for employee tax withholdings, shares	4,000	19,000	108,000	149,000
Repurchase of common stock for tax withholdings, value	$ 400	$ 800	$ 4,500	$ 7,000
Cash dividends declared per common share	$ 0.2225	$ 0.21
Cash dividend	$ 7,400	$ 7,100	14,700	14,200
Stock warrants term						10 years
Stock warrants, exercise price						$ 26.68
Stock-based compensation expense	$ 4,800	$ 5,600	$ 8,500	$ 10,213
Performance Shares
Stockholders Equity And Equity Compensation Plans [Line Items]
Performance based awards granted to executive management and certain key employees shares			100,000
Vesting maturity date			Mar. 31, 2021
Vesting period			2 years
Restricted common stock
Stockholders Equity And Equity Compensation Plans [Line Items]
Vesting period			4 years
Comcast
Stockholders Equity And Equity Compensation Plans [Line Items]
Issuance of stock warrants						2,900,000
Stock warrants issued	1,400,000		1,400,000
Stock warrants vested			400,000
Comcast | Common Stock Warrants
Stockholders Equity And Equity Compensation Plans [Line Items]
Client contract incentive related to stock warrants					$ 25,100
Accumulated amortization expense of client contract incentive related to stock warrants					$ 19,800
SEC Rule 10b5-1 Plan
Stockholders Equity And Equity Compensation Plans [Line Items]
Repurchase of common stock, shares	100,000	100,000	400,000	300,000
Total amount paid	$ 6,500	$ 5,600	$ 15,800	$ 11,300
Weighted-average price per share	$ 45.39	$ 42.79	$ 40.31	$ 44.25