CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 10,995	$ 11,142	$ 32,553		$ 29,052
Investments available-for-sale:
Net change in unrealized gains (losses) on investments available-for-sale	3,727	(2,714)	3,542		10,779
Related income tax (expense) benefit	(1,472)	1,061	(1,398)		(4,284)
Net investment gains reclassified into earnings	1	8	20		8
Related income tax expense	0	(3)	(8)		(3)
Net effect on other comprehensive income (loss)	2,256	(1,648)	2,156		6,500
Defined benefit pension plan:
Recognition of unrealized gain (loss)	240	67	791	[1]	183	[1]
Related income tax (expense) benefit	(103)	(20)	(323)		(81)
Net effect on other comprehensive income (loss)	137	47	468		102
Total other comprehensive income (loss)	2,393	(1,601)	2,624		6,602
Comprehensive income	$ 13,388	$ 9,541	$ 35,177		$ 35,654

[1] This amount is included in the computation of net periodic benefit cost, see Note 9