Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Exercise of options, income tax expense	$ 0	$ 2,051	$ 2,050
Restricted share grants, settled (in shares)	92	137	116