Earnings per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$ 19,503	$ 22,837	$ 8,352	$ 20,619	$ 12,769	$ 3,996	$ 50,692	$ 37,384
Weighted average basic shares outstanding (in shares)	32,115			31,703			31,922	31,700
Common stock options and restricted stock (in shares)	456			507			602	516
Weighted average shares outstanding, diluted (in shares)	32,571			32,210			32,524	32,216
Common shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share calculation (in shares)	247			489			328	523