Share-Based Compensation - Additional Information (Details)	12 Months Ended			72 Months Ended
	Dec. 31, 2015 USD ($) compensation_plan $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) shares	Apr. 12, 2011 offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of compensation plans | compensation_plan	2
Stock-based compensation expense | $	$ 3,542,000	$ 3,080,000	$ 2,607,000
Weighted average grant-date fair value of stock options granted (in dollars per share) | $ / shares	$ 30.30	$ 8.24	$ 6.81
Period of expense of unrecognized compensation cost, years	4 years	4 years	4 years
Equity Incentive Stock Option Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	4,258,000			4,258,000
Shares available for future grant	1,797,000			1,797,000
Maximum term of grants	10 years
Options vested and exercisable, period, in years	5 years
Weighted average grant-date fair value of stock options granted (in dollars per share) | $ / shares	$ 6.64	$ 8.24	$ 6.81
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $	$ 252,000	$ 109,000	$ 28,000
Shares granted during period	25,000	14,000	6,000
Weighted average grant-date fair value of restricted stock granted (in dollars per share) | $ / shares	$ 30.30	$ 28.02	$ 23.50
Employee Stock Purchase Plan (ESPP)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $	$ 509,000	$ 375,000	$ 562,000
Shares available for future grant	2,362,000			2,362,000
Continuous years of service	2 years
Number of additional offerings | offering					5
Stock options authorized to issue to employees	4,050,000			4,050,000
Annual earnings withheld to purchase common stock | $	$ 21,250			$ 21,250
Percent of IRS limitation	85.00%			85.00%
Maximum fair value of common stock purchased | $	$ 25,000			$ 25,000
Percentage of stock purchase price	85.00%
SERP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $	$ 538,000	$ 497,000	$ 538,000
Percentage of match participants' deferrals	25.00%
Percentage of earned income on a pre-tax basis, deferred	25.00%			25.00%
Percentage of deferral in the form of common stock	15.00%			15.00%
Full vest in matching contribution	3 years
Stock options authorized to issue	1,013,000			1,013,000
Common stock reserved for future issuance	421,000			421,000
Shares exercised and delivered	15,000			15,000
Shares issued to trustee	15,000	16,000	19,000	591,000
Stock options vested and outstanding	359,000			359,000