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																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings per Share [Line Items]
Net income	$ 1,799		$ 60,336		$ 46,148		$ 14,597		$ 11,588		$ 33,700		$ 24,244		$ 16,921		$ 122,880	$ 86,453	$ 10,938
Basic weighted-average shares outstanding																	60,533,615	40,824,420	40,797,806
Diluted weighted-average shares outstanding																	61,813,719	41,227,388	41,033,440
Basic net income per share	$ 0.03	[1]	$ 0.96	[1]	$ 0.73	[1]	$ 0.29	[1]	$ 0.28	[1]	$ 0.83	[1]	$ 0.59	[1]	$ 0.41	[1]	$ 2.03	$ 2.12	$ 0.27
Diluted net income per share	$ 0.03	[1]	$ 0.93	[1]	$ 0.73	[1]	$ 0.29	[1]	$ 0.28	[1]	$ 0.82	[1]	$ 0.59	[1]	$ 0.41	[1]	$ 1.99	$ 2.10	$ 0.27
Performance shares [Member]
Earnings per Share [Line Items]
Incremental shares																	230,437	362,509	200,164
Restricted stock units [Member]
Earnings per Share [Line Items]
Incremental shares																	33,969	40,459	35,470
Stock portion of earnings and profits distribution [Member]
Earnings per Share [Line Items]
Incremental shares																	1,015,698

[1] Per share amounts are computed independently for each of the quarters presented. Therefore, the sum of the quarterly per share amounts may not equal the total computed for the year.