Summary of Significant Accounting Policies (Calculations of Basic and Diluted EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Significant Accounting Policies [Abstract]
Net income	$ 30,260	$ 28,801	$ 21,361	$ 15,400	$ 8,712	$ 19,677	$ 11,777	$ 5,126	$ 95,822	$ 45,292	$ 107,936
Weighted-average common shares outstanding - basic									49,150	48,981	48,562
Effect of diluted stock options and unvested restricted stock									714	685	552
Weighted-average common shares outstanding - diluted									49,864	49,666	49,114
Net income per share: Basic	$ 0.62	$ 0.59	$ 0.43	$ 0.31	$ 0.18	$ 0.40	$ 0.24	$ 0.11	$ 1.95	$ 0.92	$ 2.22
Net income per share: Diluted	$ 0.60	$ 0.57	$ 0.43	$ 0.31	$ 0.18	$ 0.40	$ 0.24	$ 0.10	$ 1.92	$ 0.91	$ 2.20
Anti-dilutive securities not included above									1,132	1,372	9