Earnings per Share (Reconciliation of Number of Shares Used in Calculating Basic and Diluted Earnings per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings per Share [Line Items]
Net income	$ 46,148	$ 24,244	$ 60,745	$ 41,165
Basic weighted-average shares outstanding	62,979,660	40,822,726	56,739,012	40,802,057
Diluted weighted-average shares outstanding	63,316,291	41,218,969	57,128,020	41,143,695
Basic net income per share	$ 0.73	$ 0.59	$ 1.07	$ 1.01
Diluted net income per share	$ 0.73	$ 0.59	$ 1.06	$ 1.00
Performance shares [Member]
Earnings per Share [Line Items]
Incremental shares	302,815	355,844	298,883	305,625
Restricted stock units [Member]
Earnings per Share [Line Items]
Incremental shares	33,816	40,399	90,125	36,013