Earnings per Share (Reconciliation of Number of Shares Used in Calculating Basic and Diluted Earnings per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Earnings per Share [Line Items]
Net income	$ 11,399		$ 20,565		$ 17,137		$ 6,560		$ 1,799		$ 60,336		$ 46,148		$ 14,597		$ 55,661		$ 122,880		$ 86,453
Basic weighted-average shares outstanding																	67,608		60,534		40,824
Diluted weighted-average shares outstanding																	67,743		61,814		41,227
Basic net income per share	$ 0.17	[1]	$ 0.30	[1]	$ 0.25	[1]	$ 0.10	[1]	$ 0.03	[1]	$ 0.96	[1]	$ 0.73	[1]	$ 0.29	[1]	$ 0.82	[1]	$ 2.03	[1]	$ 2.12
Diluted net income per share	$ 0.17	[1]	$ 0.30	[1]	$ 0.25	[1]	$ 0.10	[1]	$ 0.03	[1]	$ 0.93	[1]	$ 0.73	[1]	$ 0.29	[1]	$ 0.82	[1]	$ 1.99	[1]	$ 2.10
Performance shares [Member]
Earnings per Share [Line Items]
Incremental shares																	109		230		363
Restricted stock units [Member]
Earnings per Share [Line Items]
Incremental shares																	26		34		40
Stock portion of earnings and profits distribution [Member]
Earnings per Share [Line Items]
Incremental shares																			1,016

[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.