Net Income Per Share (Details) - USD ($) 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	$ 20,395	$ 25,859	$ 28,556	$ 76,289	$ 24,655	$ 36,207	$ 24,560	$ 49,991	$ 151,099	$ 135,413	$ 84,402
Less distributed and undistributed earnings allocated to participating securities									1,759	1,875	1,517
Net income allocated to common shares									$ 149,340	$ 133,538	$ 82,885
Weighted average common shares outstanding									40,186	41,217	41,067
Incremental shares from assumed LTIP awards and conversions of common stock options									166	289	204
Adjusted weighted average common shares outstanding									40,352	41,506	41,271
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect									0	0	0