Common Stock and Treasury Stock	12 Months Ended
Dec. 31, 2017
Equity [Abstract]
Common Stock and Treasury Stock	7. Common Stock and Treasury Stock As of September 12, 2012, the Company’s Board of Directors (“the Board”) had approved a stock repurchase program authorizing the Company, from time to time as market and business conditions warrant, to acquire up to $262.1 million of its common stock. On September 13, 2012, the Board approved the repurchase of up to 7,500,000 shares of the Company’s common stock, or up to $113.0 million, in place of the remaining repurchase amounts previously authorized. In July 2013 and again in February 2014, the Board approved an additional $100.0 million for the stock repurchase program for a total of an additional $200.0 million. The Company repurchased 1,653,573 shares for $37.4 million under the program during the year-ended December 31, 2017. Under the program to date, the Company has repurchased 41,782,966 shares for approximately $493.3 million. The maximum remaining authorized for purchase under the stock repurchase program was approximately $40.8 million as of December 31, 2017. Subsequent to December 31, 2017, the Company repurchased an additional 1,346,427 shares for $31.1 million under the repurchase program leaving a maximum of $9.7 million authorized for repurchases. On February 19, 2018, the Board of Directors approved $200.0 million for the stock repurchase program. During the year-ended September 30, 2006, the Company began to issue shares of treasury stock upon exercise of stock options, payment of earned performance shares, issuance of restricted stock awards, and for issuances of common stock pursuant to the Company’s employee stock purchase plan. Treasury shares issued during the year-ended December 31, 2015 included 1,146,199, 125,026, 548,671, and 978,365 shares issued pursuant to stock option exercises, RSA grants, LTIP Performance Shares vesting, and PBRSA grants, respectively. Treasury shares issued during the year-ended December 31, 2016 included 797,140, 148,322, and 470,029 shares issued pursuant to stock option exercises, RSA grants, and Retention Restricted Share Award (“Retention RSA”) grants, respectively. Treasury shares issued during the year-ended December 31, 2017 included 1,204,559 and 560,174 shares issued pursuant to stock option exercises and RSA grants, respectively.

7. Common Stock and Treasury Stock

As of September 12, 2012, the Company’s Board of Directors (“the Board”) had approved a stock repurchase program authorizing the Company, from time to time as market and business conditions warrant, to acquire up to $262.1 million of its common stock. On September 13, 2012, the Board approved the repurchase of up to 7,500,000 shares of the Company’s common stock, or up to $113.0 million, in place of the remaining repurchase amounts previously authorized. In July 2013 and again in February 2014, the Board approved an additional $100.0 million for the stock repurchase program for a total of an additional $200.0 million.

The Company repurchased 1,653,573 shares for $37.4 million under the program during the year-ended December 31, 2017. Under the program to date, the Company has repurchased 41,782,966 shares for approximately $493.3 million. The maximum remaining authorized for purchase under the stock repurchase program was approximately $40.8 million as of December 31, 2017.

Subsequent to December 31, 2017, the Company repurchased an additional 1,346,427 shares for $31.1 million under the repurchase program leaving a maximum of $9.7 million authorized for repurchases. On February 19, 2018, the Board of Directors approved $200.0 million for the stock repurchase program.

During the year-ended September 30, 2006, the Company began to issue shares of treasury stock upon exercise of stock options, payment of earned performance shares, issuance of restricted stock awards, and for issuances of common stock pursuant to the Company’s employee stock purchase plan. Treasury shares issued during the year-ended December 31, 2015 included 1,146,199, 125,026, 548,671, and 978,365 shares issued pursuant to stock option exercises, RSA grants, LTIP Performance Shares vesting, and PBRSA grants, respectively. Treasury shares issued during the year-ended December 31, 2016 included 797,140, 148,322, and 470,029 shares issued pursuant to stock option exercises, RSA grants, and Retention Restricted Share Award (“Retention RSA”) grants, respectively. Treasury shares issued during the year-ended December 31, 2017 included 1,204,559 and 560,174 shares issued pursuant to stock option exercises and RSA grants, respectively.