Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Stockholders Equity [Abstract]
Exercise of options, income tax expense	$ 2,051	$ 2,050	$ 1,451
Restricted share grants, settled shares	137	116	188