Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Condensed Consolidated Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.01		$ 0.01
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000	20,000,000
Preferred stock, shares issued (in shares)	0		0
Preferred stock, shares outstanding (in shares)	0		0
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Common stock, shares authorized (in shares)	325,000,000		325,000,000
Common stock, shares issued (in shares)	125,040,472		124,705,786
Common stock, shares outstanding (in shares)	112,107,466		112,741,217
Treasury stock (in shares)	12,933,006		11,964,569