Capital Structure	12 Months Ended
Dec. 31, 2018
Equity [Abstract]
Capital Structure	Capital Structure Common Stock The Company has one class of common stock outstanding. During the year ended December 31, 2018, 2017 and 2016, the Company acquired 51,446, 69,154 and 17,676 shares of common stock, respectively, from employees in connection with withholding tax payments related to the vesting of restricted stock for a total consideration of $3,122, $3,267 and $807, respectively. The weighted average purchase price per share of $60.68, $47.24 and $45.65, respectively, was the average of the high and low price of the Company's share of common stock on the Nasdaq Global Select Market on the trading day prior to the vesting date of the shares of restricted stock. On December 30, 2014, the Company’s Board of Directors authorized a common stock repurchase program (the “2014 Repurchase Program”), under which shares were authorized to be purchased by the Company from time to time from the open market and through private transactions during each of the fiscal years 2017 through 2019 up to an annual amount of $20,000. On February 28, 2017, the Company’s Board of Directors authorized an additional common stock repurchase program (the “2017 Repurchase Program”), under which shares may be purchased by the Company from time to time from the open market and through private transactions during each of the fiscal years 2017 through 2019 up to an aggregate additional amount of $100,000. The approval increased the 2017 authorization from $20,000 to $40,000 and authorizes stock repurchases of up to $40,000 in each of 2018 and 2019. During the year ended December 31, 2018, the Company purchased 674,604 shares of its common stock for an aggregate purchase price of approximately $39,987, including commissions, representing an average purchase price per share of $59.27 under the 2017 Repurchase Program. During the year ended December 31, 2017, the Company purchased 761,154 shares of its common stock for an aggregate purchase price of approximately $40,187, including commissions, representing an average purchase price per share of $52.80 under the 2014 and 2017 Repurchase Programs. During the year ended December 31, 2016, the Company purchased 364,056 shares of its common stock for an aggregate purchase price of approximately $17,396, including commissions, representing an average purchase price per share of $47.78 under the 2014 Repurchase Programs. Repurchased shares have been recorded as treasury shares and will be held until the Board of Directors designates that these shares be retired or used for other purposes. Dividends The Company has not paid or declared any cash dividends on its common stock during the years ended December 31, 2018, 2017 and 2016. The Company’s line of credit with a bank could restrict, or its terms of the Notes could impair, the Company’s ability to declare or make any dividends or similar distributions.

Capital Structure

Common Stock

The Company has one class of common stock outstanding.

During the year ended December 31, 2018, 2017 and 2016, the Company acquired 51,446, 69,154 and 17,676 shares of common stock, respectively, from employees in connection with withholding tax payments related to the vesting of restricted stock for a total consideration of $3,122, $3,267 and $807, respectively. The weighted average purchase price per share of $60.68, $47.24 and $45.65, respectively, was the average of the high and low price of the Company's share of common stock on the Nasdaq Global Select Market on the trading day prior to the vesting date of the shares of restricted stock.

On December 30, 2014, the Company’s Board of Directors authorized a common stock repurchase program (the “2014 Repurchase Program”), under which shares were authorized to be purchased by the Company from time to time from the open market and through private transactions during each of the fiscal years 2017 through 2019 up to an annual amount of $20,000.

On February 28, 2017, the Company’s Board of Directors authorized an additional common stock repurchase program (the “2017 Repurchase Program”), under which shares may be purchased by the Company from time to time from the open market and through private transactions during each of the fiscal years 2017 through 2019 up to an aggregate additional amount of $100,000. The approval increased the 2017 authorization from $20,000 to $40,000 and authorizes stock repurchases of up to $40,000 in each of 2018 and 2019.

During the year ended December 31, 2018, the Company purchased 674,604 shares of its common stock for an aggregate purchase price of approximately $39,987, including commissions, representing an average purchase price per share of $59.27 under the 2017 Repurchase Program.

During the year ended December 31, 2017, the Company purchased 761,154 shares of its common stock for an aggregate purchase price of approximately $40,187, including commissions, representing an average purchase price per share of $52.80 under the 2014 and 2017 Repurchase Programs.

During the year ended December 31, 2016, the Company purchased 364,056 shares of its common stock for an aggregate purchase price of approximately $17,396, including commissions, representing an average purchase price per share of $47.78 under the 2014 Repurchase Programs.

Repurchased shares have been recorded as treasury shares and will be held until the Board of Directors designates that these shares be retired or used for other purposes.

Dividends

The Company has not paid or declared any cash dividends on its common stock during the years ended December 31, 2018, 2017 and 2016. The Company’s line of credit with a bank could restrict, or its terms of the Notes could impair, the Company’s ability to declare or make any dividends or similar distributions.