Stock-Based Compensation- Employee Stock Purchase Plan (Details) - Employee Stock [Member] - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2010
Employee Stock Purchase Plan ESPP Disclosures [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Market Price, Purchase Date	85.00%
Maximum amount of common stock that an employee can purchase under Employee Stock Purchase Plan in any calendar year	$ 25,000
Additional shares available for issuance	121,000			1,000,000
Options To Purchase Common Stock Shares	99,000	136,000	168,000
Weighted average fair value of each option	$ 10.51	$ 8.71	$ 7.91
Expected volatility	47.94%	49.41%	32.05%
Risk-free weighted average interest rate	0.43%	0.12%	0.07%