Earnings per Share Earnings per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted average common shares—basic	45,920,307	45,717,697	45,850,137	45,644,096
Weighted average common shares—diluted	46,200,757	45,922,416	46,215,047	45,915,687
Restricted Stock Units (RSUs) [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Incremental common shares attributable to share-based payment arrangements	176,658	162,153	267,620	222,996
Stock Options [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Incremental common shares attributable to share-based payment arrangements	103,792	42,566	97,290	48,595