Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Net Income	$ 36,641	$ 28,486
Average common shares outstanding - basic	27,448	27,301
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	112	68
Average common shares outstanding - diluted	27,560	27,369
Earnings per share of common stock - basic	$ 1.33	$ 1.04
Earnings per share of common stock - diluted	$ 1.33	$ 1.04
Antidilutive shares excluded from computation of earnings per share amount	22	28