Net Income Per Share (Details) - USD ($) shares in Thousands, $ 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 [Abstract]
Net income	$ 24,655	$ 36,207	$ 24,560	$ 49,991	$ 15,554	$ 19,202	$ 14,018	$ 35,628	$ 135,413	$ 84,402	$ 65,991
Less distributed and undistributed earnings allocated to participating securities									1,875	1,517	1,496
Net income allocated to common shares									$ 133,538	$ 82,885	$ 64,495
Weighted average common shares outstanding									41,217	41,067	41,668
Incremental shares from assumed conversions of common stock options and LTIP awards									289	204	94
Adjusted weighted average common shares outstanding									41,506	41,271	41,762
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect									0	0	0