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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings per Share [Line Items]
Net income	$ 60,336	$ 33,700	$ 121,081	$ 74,865
Basic weighted-average shares outstanding	62,985,517	40,829,399	58,765,381	40,814,135
Diluted weighted-average shares outstanding	64,721,657	41,250,457	59,542,200	41,182,795
Basic net income per share	$ 0.96	$ 0.83	$ 2.06	$ 1.83
Diluted net income per share	$ 0.93	$ 0.82	$ 2.03	$ 1.82
Performance shares [Member]
Earnings per Share [Line Items]
Incremental shares	269,998	378,149	262,648	331,082
Restricted stock units [Member]
Earnings per Share [Line Items]
Incremental shares	37,535	42,909	32,736	37,578
Stock portion of earnings and profits distribution [Member]
Earnings per Share [Line Items]
Incremental shares	1,428,607		481,435