Stockholders' Equity - Narrative (Details)	1 Months Ended	12 Months Ended
	May 31, 2017 USD ($)	Dec. 31, 2017 USD ($) series vote $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Authorized shares of common stock | shares		100,000,000	100,000,000
Voting rights per common share | vote		1
Shares acquired by the entity | shares		28,000	46,000	40,000
Cost of shares acquired by the entity | $		$ 2,500,000	$ 3,800,000	$ 2,500,000
Number of business days after which rights distribution date occurs		10 days
Minimum percentage of beneficial ownership interest in the entity's common stock to be achieved by a person or group for the rights to be exercisable		15.00%
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Authorized shares of preferred stock | shares		20,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.01
Minimum number of series of preferred stock to be issued | series		1
Number of preferred shares issued | shares		0
2017 Stock Purchase Plan
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Stock repurchase program, period in force	12 months
Common stock purchased under the stock purchase plan (in shares) | shares		0
Cost of shares of common stock acquired | $		$ 0
2016 Stock Purchase Plan
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Authorized amount of repurchase under the stock purchase plan | $			$ 25,000,000
Common stock purchased under the stock purchase plan (in shares) | shares		85,354	91,542
Cost of shares of common stock acquired | $		$ 6,800,000	$ 7,400,000
2015 Stock Purchase Plan
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Authorized amount of repurchase under the stock purchase plan | $				$ 25,000,000
Common stock purchased under the stock purchase plan (in shares) | shares			93,600	42,100
Cost of shares of common stock acquired | $			$ 5,200,000	$ 2,400,000
2014 Stock Purchase Plan
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock purchased under the stock purchase plan (in shares) | shares				60,900
Cost of shares of common stock acquired | $				$ 3,500,000
Maximum | 2017 Stock Purchase Plan
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Authorized amount of repurchase under the stock purchase plan | $	$ 25,000,000