Regulatory Restrictions (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital (to risk weighted assets), actual amount	$ 1,112,924,000	$ 774,360,000
Total capital (to risk weighted assets), actual ratio	12.12%	10.56%
Total capital (to risk weighted assets) for capital adequacy purposes, amount	734,385,000	586,615,000
Total capital (to risk weighted assets) for capital adequacy purposes, ratio	8.00%	8.00%
Tier 1 capital (to risk-weighted assets), actual amount	923,677,000	701,534,000
Tier 1 capital (to risk-weighted assets), actual ratio	10.06%	9.57%
Tier 1 capital (to risk-weighted assets) for capital adequacy purposes, amount	367,192,000	293,307,000
Tier 1 capital (to risk-weighted assets) for capital adequacy purposes, ratio	4.00%	4.00%
Tier 1 capital (to average assets), actual amount	923,677,000	701,534,000
Tier 1 capital (to average assets), actual ration	9.41%	8.78%
Tier 1 capital (to average assets) for capital adequacy purposes, amount	392,649,000	319,482,000
Tier 1 capital (to average assets) for capital adequacy purposes, ratio	4.00%	4.00%
Required balance at the Federal Reserve	33,141,000	28,219,000
Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital (to risk weighted assets), actual amount	948,328,000	741,595,000
Total capital (to risk weighted assets), actual ratio	10.34%	10.12%
Total capital (to risk weighted assets) for capital adequacy purposes, amount	733,959,000	586,512,000
Total capital (to risk weighted assets) for capital adequacy purposes, ratio	8.00%	8.00%
Total capital (to risk weighted assets) to be well capitalized under prompt corrective action provisions, amount	917,449,000	733,140,000
Total capital (to risk weighted assets) to be well capitalized under prompt corrective action provisions, ratio	10.00%	10.00%
Tier 1 capital (to risk-weighted assets), actual amount	800,081,000	668,769,000
Tier 1 capital (to risk-weighted assets), actual ratio	8.72%	9.12%
Tier 1 capital (to risk-weighted assets) for capital adequacy purposes, amount	366,980,000	293,256,000
Tier 1 capital (to risk-weighted assets) for capital adequacy purposes, ratio	4.00%	4.00%
Tier 1 capital (to risk weighted assets) to be well capitalized under prompt corrective action provisions, amount	550,470,000	439,884,000
Tier 1 capital (to risk weighted assets) to be well capitalized under prompt corrective action provisions, ratio	6.00%	6.00%
Tier 1 capital (to average assets), actual amount	800,081,000	668,769,000
Tier 1 capital (to average assets), actual ration	8.16%	8.37%
Tier 1 capital (to average assets) for capital adequacy purposes, amount	392,433,000	319,427,000
Tier 1 capital (to average assets) for capital adequacy purposes, ratio	4.00%	4.00%
Tier 1 capital (to average assets) to be well capitalized under prompt corrective action provisions, amount	$ 490,541,000	$ 399,283,000
Tier 1 capital (to average assets) to be well capitalized under prompt corrective action provisions, ratio	5.00%	5.00%