Employee Benefit Plans (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) installment $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares	Dec. 31, 2008 shares
Defined Benefit Plan Disclosure
Employer contribution for defined contribution plan | $	$ 1,000,000	$ 900,000	$ 700,000
Employee Stock Ownership Plan, common stock, shares outstanding (shares) | shares	155,309
Employee Stock Ownership Plan, common stock, fair value | $	$ 14,100,000
Employee Stock Ownership Plan ESOP Plan
Defined Benefit Plan Disclosure
Employee Stock Ownership Plan, service period eligible to participate (years)	1 year
Participants vesting percentage after three years of continuous service (percent)	100.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Initial Public Offering
Defined Benefit Plan Disclosure
Contribution to Employee Stock Ownership Plan, common stock (shares) | shares				22,500
Outside Directors
Defined Benefit Plan Disclosure
Number of deferred common stock (shares) | shares	8,466	9,415	7,173
Weighted-average grant date fair values of deferred common stock (dollars per share) | $ / shares	$ 78.62	$ 70.63	$ 66.77
Nonqualified Deferred Compensation Plan
Defined Benefit Plan Disclosure
Deferred compensation expense | $	$ 106,000	$ 82,000	$ 46,000
Number of annual installments of deferred compensation (installment) | installment	2
Number of days after departure from board of directors for payment of deferred compensation (days)	90 days