Operations and Significant Accounting Policies (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 [Abstract]
Net income	$ 14,933	$ 6,970	$ 5,695	$ 1,021	$ 15,653	$ 5,825	$ 8,719	$ 10,657	$ 28,620	$ 40,854	$ 55,487
Basic-weighted average shares outstanding (in shares)									28,325	28,118	27,939
Effect of dilutive potential securities (in shares)									1,170	772	232
Diluted-weighted average shares outstanding (in shares)									29,495	28,890	28,171
Basic EPS (in dollars per share)	$ 0.53	$ 0.25	$ 0.20	$ 0.04	$ 0.56	$ 0.21	$ 0.31	$ 0.38	$ 1.01	$ 1.45	$ 1.99
Diluted EPS (in dollars per share)	$ 0.49	$ 0.23	$ 0.19	$ 0.04	$ 0.54	$ 0.20	$ 0.30	$ 0.37	$ 0.97	$ 1.41	$ 1.97
Shares excluded from computation of earnings per share									700	700	1,200