(Details 8) - 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
Accounting Policies [Abstract]
Net income (loss)									$ 63,116	$ 65,584	$ 72,940
Weighted average common shares, basic (in shares)									48,168	48,060	48,009
Weighted average common shares, dilutive (in shares)									48,168	48,060	48,009
Earnings per share—basic (in dollars per share)									$ 1.31	$ 1.36	$ 1.52
Earnings per share—diluted (in dollars per share)	$ 0.24	$ 0.88	$ 0.35	$ (0.16)	$ 0.32	$ 0.75	$ 0.31	$ (0.02)	$ 1.31	$ 1.36	$ 1.52