Retirement and Other Employee Benefits - Employee Stock Purchase Plan (Details) - $ / shares	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Actual return on plan assets:
Shares available for issuance	656,737	685,996
Employee Stock Purchase Plan
Actual return on plan assets:
Common stock purchase price to eligible employees (as a percent)	90.00%
Percentage of Black-Scholes methodology used as a component to calculate value of lookback feature	90.00%
Percentage of maximum subscription price used as a component to calculate value of lookback feature	10.00%
Shares available for issuance	707,735
Subscriptions outstanding (in shares)	25,407	59,529
Maximum subscription price (in dollars per share)	$ 30.29	$ 21.43
Shares of stock issued	56,908	56,193
Stock issuance price (in dollars per share)	$ 21.09	$ 21.01
Assumptions for valuation of shares
Fair value of grants (in dollars per share)	$ 6.11	$ 3.58
Risk-free interest rate (as a percent)	0.70%	0.26%
Expected dividend yield (as a percent)	3.10%	4.40%
Expected volatility (as a percent)	27.00%	21.00%
Expected life in months	12 months	12 months